We know, from the game's lore, that there are at least two kind of Dragons, red and black. They are worshipped, or at least highly respected, by the Empire. They are intelligent, can speak and can work for the Empire (from Redguard) to survive. They were drove off from Morrowind by Cliff Racers and hunted into close extinction by the vampiric snakes, the Tsaesci.

Skyrim dragons are brown, don't seem too keen on negotiating with anyone and are heralds of Alduin and the end of the world so not too keen on self preservation as well.

So are Skyrim Dragons different from the, let's say, normal Dragons? If natural Dragons are allies of the Empire, then are Alduin's servants free game because they want to, well, kill everybody?

Actually, Im pretty sure the dragons of alduin are black (supposedly..), and are called jills... Atleast I read in a GI article ( I think...) that they were black and called jills, though I know I read it somewhere...

Yes, they looked brownish to me but the one on the trailer is black. And I recall them being the Jills of Akatosh as well. So maybe being the Jill means they are not your run of the mill dragons.