Lususes have coloured blood too though? It’s present frequently in the comic (specifically seen the best in Eridan’s early panels, where he shoots a whale lusus that spurts out violet blood). Unless you’re talking about their fur/pigment..? White paint is honestly a mystery irl too.

Yeah, their blood is colored like the Trolls’ Hemospectrum, but they may be able to get pigment from their bodies. Specially insectoid Lusii, I’d imagine.