Hey, um, for oc reasons: let's say there is a troll whose shade of blood is just so unfortunately coloured that most aren't sure whether it's a violet or a fuchsia. What would happen? Would they just give the troll to a violet blood lusus or to the fuchsia one (can't write the name right), or would they be like "Eh, guess it's defective or some shit" and cull it? Or is this scenario entirely impossible?

Non-standard hematological attributes are an on-sight cullable offense. They would grow up Lusus-less, if someone even allowed them to live/raised them a-la Dolorosa or like Bronya.