I look best in purple, hot pink, or spring green, which is somewhat unfortunate since I'm a bio-female, who crossdresses as male. I definitely look more feminine when I wear those colours.
Dressing male I tend to wear black, dark green, red, brown, and grey. So, dark colours.
All gender boundaries set aside, I love any colour, but right now I'm tending towards red and purple (especially light red and mauve or eggplant).