I like this question. Forces me to think about each item to see what I think. Here goes.
For rainflys and tarps, jackets and coats I like royal blue. It picks up the color in my blue eyes. Here's a pic.

For pants, gloves, stocking caps, etc. I like black.
For sun hats- tan with darker color under visor to reduce relection.
For inner tents-white for light
Sleeping bag-lighter colors so I can see if there are any critters inside
stuff sacks-don't care but like different colored ones so I know what's inside
Backpack-I like the look of all black. Also hides dirt. It's easier to find something in a white pack but they show dirt and wear. Torn on this one.
Socks-white so I can spot bugs and ticks easier but prefer black for not showing dirt
Looks like I'm conflicted on some items between function and looking undirty. So if I'm going alone and won't see people I'll go for function. If I'm walking in Scotland with my wife I'll be forced to consider colors. Generally I prefer to ignore the colors of things except for function.