Check out the last question/answer from the Blizzard forums here.
12-18 color choices in normal gameplay, plus custom colors in the map editor. Hot, M I RITE?

On another note, they mention Firebats in the current build of the game and some discussion of possible special abilities. Three Marine upgrades to help them combat late-game units. Interesting stuff.

Yeah, that is hot. The regular colors that werent able to be chosen without scmdraft were getting a bit too old, except the color purple. If they add the colors from scmdraft, guedit, and etc, that would be just plain gay.

18 colours is ok I guess... but hopefully they wont just take the warcraft3 colours, and add "metalic" versions with them...

Starcraft I had alot of colours too. Or wait does Starcraft 2 have more colours than its predessor?

Starcraft do need those metallic colors. It suits them, but it might ruin the color of players so it is unlikely.

Colours I want are

1- Red
2- Blue
3- Teal
4- Purple
5- Orange
6- White (REAL WHITE)
7- Yellow
8- Lt.Green (war 3 green)
9- Lt.Blue (Neutral Unit)
10- Pink
11- Brown
12- Silver (Hidden Dark Templar Tribe, DUN DUN DUN!)

Reasons for the colours?

Red is the dominion, hero zerg, and is nice
Blue is protoss everything, and Jim Raynor, and looks cool
Teal is hero units, (they might change this though) and is Dark Templar colour
Purple is Zerg, and nice
Orange is just a filler colour, I dont really care about it
White is the UED and is another cool colour
Yellow is the Protoss Judicator and Looks cool
Lt.Green would be a great new colour for both melee and campaign (Green zerg or protoss!)
Lt.Blue would be an amazing melee colour, and could Serve as another protoss tribe
Pink, I dont know, but it still seems like a cool colour to have
Brown, zerg, zerg, zerg, DURAN!, zerg, zerg, zerg
Silver the Ultimate colour, and ***ZERATUL'S LONG LOST TRIBE?!***

considering how much theyre saying the starcraft 2 editor will rock it is interally possible that in the map editor how they said u can make factions any colour, seems to me like a possiblecolour wheel/grid involving RGB,hopefully also having an option for metallizing a colour

Just thinking about that makes me drolling.

Maybe complete customizable colours, not just RGB alone, but the flexability of adding basic colours to each other, then converting that colour to light?