The DM is also perfectly within his rights to keep damage types as they are. As you pointed out you have a bunch of feats that work off the cold keyword. If they wanted those to be used with Blood Pulse they'd have either given blood pulse the cold keyword or not forced the feats to work with a specific damage type. The DM is totally within his rights to keep things at the status quo.
You can flavor the power however you like of course, however the damage will still technically be untyped.
Lasting Frost, will still apply the vulnerable 5 cold, which will trigger the rest of yourself. If the creature only has resist 5 cold, then they will effectively cancel each other out (except you still get wintertouched bonus).
When you play a damage type theme, sometimes you have to deal with things that aren't necessarily your forte. Just like a hammer isn't always the answer, neither is a snow cone.
Also looking at the Aspect of Tiamat, its made to cancel out a majority of elemental effects (Resist 15 acid, 15 cold, 15 fire, 15 lightning, 15 poison). So almost anyone who plays with elements has to start thinking outside of just throwing powers at it.
It's the cost of having a limited variety of abilities. You'll just have to look for abilities that let you pierce resistances. There are plenty of them.
This^^. Some versatility is always a good idea for this exact reason. Now I'm sure you wouldn't complain if the creature had vulnerability cold, so if it has resistance you just need to suck it up. Look at it this way, in previous editions a lot of creatures had immunity instead of just resistance. You at least have a chance to overcome it now. If you love your character concept that much, then accept its innate weaknesses. I don't mean to be a dick here, but did you honestly not see this coming? Should the DM never ever use cold resistant creatures?
I think you need to realize that the game isn't just about you.
As long as the DM doesn't constantly bombard you with creatures resistant/immune to cold, you shouldn't complain.
The fact that the aspect of tiamat has resistances to every element, not only cold, makes your argument of being singled out weaker. This solo is designed to be hard for everyone to take down.
Edit in: Whoops missed your comment on the blood mage. Yea, the DM is fair in keeping the damage normal instead of cold based. The ability becomes way more powerful than it is meant to be if you alter it in that way. You shouldn't expect abilities to change to make you more powerful.
You specialized in a particular type of attack - in this case dealing cold damage. Some foes have resitances. This one just happens to have cold resistance....
So yes, pointing, "You deal less damage". Btw, how is that NOT a challenge?
Things that are easy to do are no challenge.
Good luck.
LIFE AI'NT FAIR
I agree, it's better to have a greater variety of elements at your disposal. Also you could also get powers with non-elemental keywords like "Mesmeric Hold" which does not have an element. In other words...
LIFE AI'NT FAIR
That. Facing resistances are part of being a wizard. Sometimes you get the short end of the stick. Cold is a fairly common resistance type. Force and psychic, much less so.
i am only looking for a consensus here. in one of my games i am playing a frost wizard, staff with three feats for cold spells (student of moil, wintertouched, and lasting frost). our dm started off the latest session with a boss encounter against a solo (aspect of tiamat). when i inquired whether my blood mage pp ability to deal ongoing damage coulde be cold damage, he told me i wouldn;t want to do that anyway because he has resistances. That made me really upset, because it ruins my character concept. i cant use the char to its fullest. now i don't have a problem facing other mobs with resist cold, cause the others can deals while i attack other mobs, but a solo? it doesn't come off as an interesting challenge to over come. its like he points and says "you deal less damage"
So you decided to specialize is a specific damage type and are now upset when a creature happens to have resistance to that type?
I am not normally a mean person but the answer here is "Suck it up."
Seriously. Be glad it doesn't have immunity.
Now if you consistently have enemies with resistance to your damage, then it's a sign of a vindictive DM, but if it happens once or twice, it's just him giving you a balanced set of enemies. If you specialize, you are willingly taking a weakness in exchange for a strength, and as such it is in the DM's interest to both give you opportunity to have your strength shine and have your enemies exploit your weakness.
Specialists are cool, but they're also limited. You specialied in cold spells of your own fee will. Yes, it's fair for a specialist to occasionally be hindered or even useless because what you're fighting is immune to whatever you chose to specialize in. That's the cost of specialization.
QFT. Big time.
I highly recommend retraining some powers and feats over your next few levels. It's apparent that you need to explore some new options in the 'killing stuff' department. Maybe something involving necrotic damage, so your student of moil feat would still help you. Or an at-will that does fire damage combined with the arcane fire feat. (which will work nicely with your cold-based feats, actually.)
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For what it's worth, I feel your pain. The last two times I used my armor of agathys daily, my opponents had cold resistance. I used it anyway, cuz I needed the temp hit points badly. But it did no damage whatsoever. 
when i inquired whether my blood mage pp ability to deal ongoing damage coulde be cold damage, he told me i wouldn;t want to do that anyway because he has resistances. That made me really upset, because it ruins my character concept.
Your DM helps you out by telling you that by making that change would make your character less effective vs that monster and you are mad at him? I'm just completely astounded by the stupidity of this.
and for the record: i was unsure if the damage from blood pulse was untyped; i do have some necro spells; im[u]not[u] asking to never throw cold resist against us, just give me something to do to deal with it, or other mobs; and i know life ain't fair, but this is a game!
Also, did you see the stats posted for the Aspect? It's has Resist 15 cold, so your Blood Pulse does more damage to it untyped. Why would you want to gimp yourself by making it cold damage?
Bottom line: if you think the DM is being unfair to you, then talk to them about it after a gaming session. They might not be taking into account all of the work you've put into being a frost mage. And, if you've been talking about it often enough, they might be throwing these cold resistant monsters at you to help your character have some more challenge during the fights.
thanks for all the feedback. i genuenly apprieciate it all, but i think some of you miss the point. the point was not the damage, it was the fact that being the only one who deals alot of elemental damge, i was being singled out. and our dm has run an entire adventure with cold resistence mobs, so thats not the point either. but i feel that it can be so easy to create a way to deal with the issue, and the dm wouldn't work with me on it. i spent three of my char's most precious resource on being better at something, only to be shortchanged again. i inderstand its within his rights to do to the group, but i also feel its within my rights to ask him to at least give me a way to deal with it (ie something thats providing the resistences that i could destroy, ect)
and for the record: i was unsure if the damage from blood pulse was untyped; i do have some necro spells; im[u]not[u] asking to never throw cold resist against us, just give me something to do to deal with it, or other mobs; and i know life ain't fair, but this is a game!
Oh no! An entire adventure full of frost resistant enemies?!?!? Haven't you ever encountered this in other games? I could probably name a dozen or so video games that have some part that completely screws one class. Older editions had MR/SR, elemental immunities, or anti-magic fields.
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Good thing you aren't an old school WoW raider. First three years of the game screwed Fire mages. If it wasn't about three 40-man dungeons full of fire immune enemies than it was everyone pvping in fire resistance gear. On second thought, you do whine and cry as much as an old school WoW mage.
"and our dm has run an entire adventure with cold resistence mobs"
...That's what I read. I could be mistaken, but assuming that sentence is correct, my comments are completely valid.
You are mistaken. The only part that talks about anything but the Aspect of Tiamat (one fight) is the part where he says:
i don't have a problem facing other mobs with resist cold, cause the others can deals while i attack other mobs
It gives no information on the quantity of those mobs and it's obvious there were other non resistant monsters present.
In addition as I said before he has non cold powers, and he's complaining because the GM won't let him make them cold based so he can keep this Winter's touch/Lasting Frost combo going.
"and our dm has run an entire adventure with cold resistence mobs"
...That's what I read. I could be mistaken, but assuming that sentence is correct, my comments are completely valid.
And as you said, everyone is being completely ruthless and a dick even though they don't need to be. Even if it's not the case.
So it's perfectly fine to wank and dick around about critical fumbles, but when some guy comes on and makes a really incoherent post about a DM having the audacity to throw monsters around that his character is weak against, and a couple people tell him to suck it up, THAN YOU'VE GONE TOO FAR!
C'mon dude, it's only words on the internet. Come down off your gleaming white horse for a minute or two. :D
Plus, I had that WAAAmbulance picture just sitting around gathering dust for the longest time, I couldn't just let it go to waste, now could I? :D
You are mistaken.
That was a DIRECT QUOTE from his follow up post. How could my direct quote be mistaken. o.O
And what's the whining about? +2 to attack with combat advantage? The OP is playing a Wizard, so that CA is not going to do anything more for him than the +2 to attack. Granted, that could mean the difference between a hit or a miss, but it's still only +2 to attack. If it was a Rogue with a Frost Weapon and this set up and going through all of this, then I could see cause for him to complain a little bit. But the combo listed (wintertouch + lasting frost) still gives the vulnerable cold even if the monster has resist cold, so you still get the +2 to attack with cold powers. You won't get all the damage through, but you *will* get your combat advantage.
i am only looking for a consensus here. in one of my games i am playing a frost wizard, staff with three feats for cold spells (student of moil, wintertouched, and lasting frost). our dm started off the latest session with a boss encounter against a solo (aspect of tiamat). when i inquired whether my blood mage pp ability to deal ongoing damage coulde be cold damage, he told me i wouldn;t want to do that anyway because he has resistances. That made me really upset, because it ruins my character concept. i cant use the char to its fullest. now i don't have a problem facing other mobs with resist cold, cause the others can deals while i attack other mobs, but a solo? it doesn't come off as an interesting challenge to over come. its like he points and says "you deal less damage"
Whether you're doing big damage or average damage, you're still knocking hit points off the monsters, and in the end dead bad guys are dead bad guys, no matter if it took a few more turns to get them that way. It's hardly "ruining (your) character concept".
I believe you may not be attaching the appropriate significance to the "extra" part of the statement, "I'm not going to be able to deal my extra damage.", which is basically what you're saying...
Being "less effective" against a monster (especially when it's the only bad guy in a fight) may suck, but you have to look at it like this:
The effort involved in specializing in one particular type of elemental damage or in one particular combat trick gave you something "extra", above and beyond the "average". Without that, you're not gimped or handicapped, you're just... "normal".
A normal paragon-level ass-kicking magic-slinging wizard.
"I hit him with my sword. Again.", may not sound as cool as, "I hit him with my Icy Blue Ray of Doom and freeze his eyeballs until they explode!", but thirty years of games played by thousands of players have proven that a plain old vanilla basic melee attack is still a perfectly respectable way to win a fight.
I played a lot of rogues in 3.5 and earlier editions.
Back in the old days, skeletons took only took one point of damage from non-bludgeoning weapons. Kind of hard to backstab them with a shortsword.
Not wanting to be "ineffective" against them, I simply bought a mace and a sling and happily banged away at them 4 or 5 hp at a time, turn after turn, just like everybody else in the party.
As far as the fight with the solo monster with cold resistance, you should be asking yourself why it didn't seem like an interesting challenge. Because your big "theme" gimmick wasn't as awesome and effective as you wanted it to be? You should always expect that when creating a character uber-specialized in one particular area, there will be situations where your particular trick won't be the most effective solution - no matter how good you are at swinging a hammer, it doesn't make you any more effective at tightening screws.
I personally find it much more interesting when my characters are faced with challenges that their usual tactics can't easily solve. I can then revel in how awesome and smart I am for being adaptable and having a Plan B. And Plan C. And D.
In my experience, when playing an elemental-themed wizard you should have only about two-thirds of your powers/spells/abilities/whatever focused on your particular element, and the remainder focused on alternate means of being effective, for those situations where your elemental focus is a hinderance rather than a benefit.
Thanks!