I'd assume the black is silicon carbide, and the pink is likely aluminum oxide (AlOx is often found in white, pink, blue colors). Aside from the green compounds, those two are probably most common for use on steel. You're likely correct, in assuming the green is chromium oxide. Grit size is anybody's guess, as silicon carbide and aluminum oxide can be found in a very wide range of sizes. If JRE doesn't even know (or is unwilling to say), that's not a very encouraging sign for JRE. I'd either avoid them, or be more persistent about making them find out more of the specifics. It may be that their compounds work well enough, and maybe better in their recommended sequence, but I generally don't like using compounds for which I can't reasonably predict how they'll perform (and that's dependent on knowing type & size).
