Well… some of the icons I’m doing are not fixed colors, but transparent dark or transparent white, (not sure I can play with blend modes, but that’s next to test) which means that even if I try lots of different funky colors in my theme, the icons will still blend more or less nicely:
Now, I suggested here that rather than having to change 100 individual colors and leaving it up to the user to find a good balance (and find what to change), it would be better to be able to just have a few base colors and a contrast slider, so maybe that’s at least something you could try for the grid?