First and foremost, whatever is on sale because it's usually what no one else wants. Fine for me.
Given a choice, I like a brightly colored shelter so I can find it and because it looks more cheerful inside. I try to avoid the paramilitary look. I get enough of that at work.
For clothing, light colors to reflect the sun in the summer, dark colors to absorb the sun in the winter.
I like black for a sleeping bag because it seems to absorb heat and dry out faster in the sun. No science behind this, just my observation.
If you only travel on sunny days you will never reach your destination.*
* May not apply at certain latitudes in Canada and elsewhere.