I've always been a sucker for blue....but depends...if you like the devil, and are evil, then with red, and plaster your case with the number sequence 666. or if you're a hippy, go with yellow, you flower girl
I was going to go for blue in my case but i found out that my mobo AN8 Ultra has red leds build in so i went with red. It still looks hot but i can't find a key board that glows red, they all glow blue. so im waiting for a red keyboard... so i you want every thing to match then go with blue.
i have a mix of everything. i have blue and redinside my PSU which gives purple'ish, green on the back, red on the side, Blue neons and green neons. he he he, i like lights.