[quote=Guru]
but then again... I'm not really sure what you said about black. O.o XD
[/quote]

Don't paint with black or white -- they make your colors look muddy/dead. Take the guy's skin for instance... Using black to add in your shadows has caused your skintone to look very muddy and unrealistic. Only paint with colors that have saturation to them! 

In real life there is actually never a true black or white color -- they are always reflecting or absorbing the colors around them, which then gives them their tint. When you add in either black or white to a colored painting, your eyes automatically know it looks wrong because you'd never actually see those colors in the real world. (Even a super dark area or a super bright area will always have some saturation to it.) Add your highlights and your shadows with a more lively color (rather than mixing in black or white ) and you'll add a definite notch of realism to your color work.