Rotten Yellow vs Ushabti Bone

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Ushabti Bone is noticeably darker, more muted than Rotten Yellow.

Can I use Ushabti Bone instead of Rotten Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ushabti Bone is noticeably darker, more muted than Rotten Yellow.

Can I use Rotten Yellow instead of Ushabti Bone?

The same difference applies the other way round: Rotten Yellow is noticeably lighter, more saturated.

ΔE is the colour difference between our two swatch estimates: under about 6 is close, over about 15 is loose. Real paints also differ in finish, coverage and how they thin, so test before you commit.