Red!
For the reasons Diana says, actually. It's dominant, it's romantic and it's sexy. >:3 It goes great with my other favourite colour, black. [Well, it's a shade, but... Whatever.] It's very strong, too, for representing anger. I'm unhealthy in that sense; I bottle up my anger and then have a rage. So I turn red, so to speak.
It's been my best colour for as long as I can remember. Ever since I was a very little girl. My favoured markers, crayons, stickers, etc. were red. When we took family photos, I'd always wanna wear red.
Also, it is the colour of blood and Sith lightsabers. Muahaha. <3