Shit, this exact question was up here a month ago or so.
When I was still teaching SDM's, we had tons of steel (literally) and would setup E, F and pepper poppers out to 1k (600m for the students with an extra few out to 1k for us to fart around with whatever toys we brought to work, which is another story).
When we taught 'em how to spot and range, etc., (they were using ACOGs) one of the important things for determining range was the color of the target contrasted to the background. Basically the brighter the target looks the closer it appears and the darker it is the farther out it appear. Mostly true for warm colors but high chroma colors will also appear closer. For instance, a yellow target against grass will always appear closer than a brown target against grass.
They were learning to use ACOGs and rely on the ranging reticle for the most part, but they also had to do some basic range estimation too (and compare that against the ACOG to give them confidence in that reticle). What was the most interesting was when we'd use a wide range and have targets all over the place. Some were the same distance, different color and chroma. Without the ACOG or some other kind of ranging method other than guesstimation, the targets at the same distance but different colors were almost always figured to be different distances. Of course the two targets cannot be right next to each other.
So we used all kinds of colors, but I recall brown and tan being used the most along with green. Probably because real life targets will likely be wearing those colors.
Bottom line is just beware how the different colors work with respect to range estimation.
IME, bright colors show hits the best with white being the most obvious, provided they expose the steel or leave a good mark when the bullet disintegrates.