An oddly specific scenario indeed. So much so that it only happened once in all of Alternia. Well. Twice. Technically.

"Well. Those at the top of the spectrum use those at the bottom. Rust to yellow is usually slaves. Psii--he was a slave basically. Sort of. I mean, he did factory work and he had no choice in the matter. He had hardly enough to eat. Olive up aren't usually slaves, but...every caste tends to be used by the ones above them and use the ones below. And you better believe trolls take advantage of it. 'At least I'm not a rust or a brown', a yellow might say. But a green or teal or blue might be keeping them as a servant, using them or killing them as they desire. You don't need to justify killing someone below you. You might get a slap on the wrist if they were someone's property but then again they might say 'it's only a lowblood'. They see the lowest bloods as replaceable. And don't get me started on indigos. Violent ruthless clown monsters."

She's worked up again, mouth twisted in a snarl, "That's why we thought you were lying. A joke, to think the Empress might take a rust as an adviser. The Condesce wouldn't deign to see a rustblood in her presence, let alone take one as a trusted friend."