The trouble with so many of these asks is that I'm not being evasive and indecisive, but context plays such a large part in most of the answers that I feel as though I'm leaving people hanging when I actually answer them!
If there's a colour combination I like which will work on just about anything? Blue and yellow. It's hard to go wrong with those two no matter what they're on, and blue and yellow are a colour combination which a lot more people can see than some others; most people that're colourblind in some fashion can still usually see blue/yellow pretty well, so I've come to just like it.
Orange and white is another really nice combination that I like on a lot of things. In an ancient Star Wars D20 game I was involved in, my pilot had an R2 droid with a defective binary vocalizer unit called Tweak. Tweak was white, and nice, bold orange where R2D2 would be blue. I was doing it way before BB-8!