For anyone who is interested: standard NATO tracers use Strontium Nitrate (Red) and Russian/USSR/Chinese Tracers use Barium salts (Green- not in the game), so the close-est would probably be Sodium Chloride/Copper Chloride. I use Strontium myself, though I do wish it was a little brighter. Real tracer rounds are mixed with Magnesium to give them more visibility.
Is that like the natural flame color of the casing? I thought you added dye to the slugs, in which case it's a simple matter of mixing different metals dyes together to get a preferred color.
Burning metals does not work that way. to get a certain color, you have to take elements which emission spectrum meets the color you need. While it is true that you can get two different things together and they will mix color, it is not as simple as "adding dye to the slug". For example, a Pink colored metal could still burn dark red or blue.