7 Paint colors.

[Marcem]

yellow, green, blue, red, black, white, brown

This. 

[Ad Bot]

[Hugums]

Black, white, three shades of grey and two transparent ones.

[_Rebel_]

That would suck.
Red, wood-brown, dirt-brown, green, blue, transparent blue, 75% gray.

[Niliscro]

Blue, Green, Red, Black, White, Gray, 25% White.


Edit:
Osht no brown :c

[Camera]

White, Lite Gray, Gray, Dark Gray, Black, Trans Black and Trans White.

That's about it.

[Flying Ace]

I would mix the main colors to make any color 

[LegoEggo]

Darkish purple and 6 shades of gray

[Chrono]

Red, blue, yellow, green, purple, orange, and pink.

[M]

Two browns, two grays, two greens, and a trans blue.
(Dirt/wood, stone, grass/leaves, water)

[Colten]

Black
Grey
White
Brown
Tan
Green
Transparent Blue

[tapemaster21]

Red
Orange
Green
Blue
Purple
Black
Brown

[Visage]

Brown, green, dark grey, black, blue, white, transparent(the glass-looking one).

[Hectic]

I would mix the main colors to make any color 

but you might Screw up and end up with one shade of brown all your life.

[Azazel]

Pink, pink, pink, pink, pink, pink. Oh, and pink.

[kidpower]

gray,transparent glass color , blue,red,green,orange,brown