Honestly it depends, i didn't really think of that!
I played a lot of sacred Stones as a kid and I vaguely recall everything having a background box of some sort. It's been a while though.
Try it out over a couple backgrounds, you might be able to sidestep any problems entirely if you make proper use of negative space if it's not working out there!
Obviously not always a solution, of course, forest environments would be troublesome for example. The colors should be dark enough for contrast in most cases, maybe keep the original around as an alt for tricky environments?
On my phone, sorry for rambling!