Ushabti Bone vs Sickly Skin

How close are they?

ΔE 17.4, loose: different enough that you should pick on purpose. Sickly Skin is noticeably lighter, more saturated, cooler than Ushabti Bone.

Can I use Sickly Skin instead of Ushabti Bone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Sickly Skin is noticeably lighter, more saturated, cooler than Ushabti Bone.

Can I use Ushabti Bone instead of Sickly Skin?

The same difference applies the other way round: Ushabti Bone is noticeably darker, more muted, warmer.

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.