assuming the non-striated hemocaste system (ie: assuming colors are not distinct and instead there's variation within castes, and cuspcaste trolls), i'm sure there's something akin to the munsell color system for blood as opposed to soil. trolls are exclusive and crabby enough i can totally imagine troll craigslist (casteslist?) being full of personals like "7f g17 for h16 and above ONLY". or clubs that make u colormatch at the door to prove you're highcaste/pure enough to get in. like, "oh, sorry, you're a solid 21 teal which is fine, but you're so dim.. h or i, for sure.. too bad, sucker!"
fwiw this idea would also have to assume that trolls can have dimmer or purer blood - ie cleaner, more true hue blood vs. muddier, dimmer, grayer blood. which seems perfectly reasonable to me.
it also ties into an idea i've been nursing for a while about lower castes having more limited lifespans having to do with whatever minerals/elements make their blood that color. rusts and bronzes have relatively comparable human lifespans, indicating they probably have similar iron-based blood, but as you go up the caste ladder, the minerals and compositions change towards things that don't oxidize over decades and centuries (or perhaps they've evolved to create more telomerase in the higher castes? or maybe the mother grub is even capable of artifically selecting for that?)