Which color is best for male shirts or pants?

Nothing wrong with White. I have seen a few men wear a pink dress shirt, and that is sexy as hell.

Not a girl but I'll answer anyway

By "shirt" do you mean formal button-up shirts, or fashionable t-shirts? Either way, you can't go wrong with white, black, grey or blue because they're very neutral and go with almost anything. Light pink is also very popular for formal shirts. For casual looks I also like purple.

Trousers/"pants" (I'm British) - For formal, stick to grey, black or dark blue. For casual, slim-fit chinos in any colour are fashionable this decade, but personally I prefer the beige-y colour or light grey ones on myself. You also can never go wrong with any kind of blue jeans as long as they're not a dated or unfashionable cut for the time.

Matching your shoes, hat and other accessories to either your shirt or "pants" is also a nice way of bringing the look together. Ideally your shirt and "pants" should never be the exact same colour unless both are black (acceptable).

Depends on the situation and circumstance. I don't think theres a single answer that is applicable across the entire fashion spectrum.

Studies have shown that women prefer men in red. http://www.rochester.edu/news/show.php?id=3663

Black shirt, camouflage shorts, any colored socks, white/black shoes