I have seen so far two kind of dragons cold breath and fire breath but both look the same skin is that right? or I missed some details? Also there are other variations?

There are six types of dragons, design wise, which appear based on your level. (Ranging from weakest to strongest) There are regular dragons, blood dragons, Elder dragons, and Ancient dragons. (I missed a couple...) And each one can have either fire or frost breathe I'm pretty sure.

Dragons also come in many colors, as well as by name. Green dragons are weaker than red and bronze-skinned dragons.

I have only seen the same but I am not to far into the main quest yet. Can't you tell a frost dragon because they have frost patches over it's scales? I haven't paid much attention, I'm to busy running away.

An NPC told me about 4 different ones that I can remember off the top of my head: copper, green, gold, and brown. They didn't refer to them as blood or elder or ancient, but it seems to be all over the wiki pages, so I guess go with that. But definitely a good number of different ones ranging in strength.

i've run into blood dragons they are bigger then the normal one and their heads sorta resemble clanfears heads from oblivion also their tale looks like a paddle

6 main types of dragons, as Todd Howard said. Though, I've only encountered 2 different types. 3 dragons were 'standard' looking like the first one Todd fought in the demo, the other one was http://images.wikia.com/elderscrolls/images/1/1b/Blood_dragon.jpg.

Dragon, Blood Dragon, Frost Dragon, Elder Dragon, Ancient Dragon, Skeletal Dragon(1 of a kind quest..)
Those are the ones I've encountered myself.

What are those named ones? Elder dragons?