Best guesses the fandom has for secret limebloods are Marvus and Boldir; think it's either, or both, or someone else?

Nah, I don’t think Boldir has any reason to hide her caste if she’s already showing herself off to be a sneaky private investigator sort of deal. Marvus’ idea of him not being Purple stems from ‘Xoloto’ -> ‘Xolotl’, which while a cool idea, I think it’s more likely he doesn’t give much of a fuck about the Purple Religion, if anything. I just think we haven’t been shown the Lime yet.