So here's color transitions between Hemospectrum castes, based on aspect.
Prospit signs are lighter, Derse signs are darker.
A True Sign (or its Prospit equivalent) will always be the base color of the sign in canon. All hues and signs in-between are based on the order it takes to get from one True Sign and its aspect, to the next caste's True Sign and aspect.
Basically it's a bunch of stupid, complicated horseshit, and you're better off just looking at this chart I made instead of me trying to explain this through text:
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Here's the signs chart, itself:
If the forum embeds are too small for you, copy image url > paste url in new tab. Or just right click / long press / whatever Macs do and select "view image."
"But SL, the colors are too close together. Wouldn't this confuse the entire Hemospectrum?"
Yup. Probably would.
But that's why it's fanart my dudes.
Also this is operating with the understanding that you have to meet a certain absolute hue value to be of a certain caste. Which is why they all start at the base / True sign.
I also colored Karkat's sign for point of reference. I know he's technically not supposed to have a caste-based one in the 'spectrum.