Burnt Umber vs Ink Skin

How close are they?

ΔE 15.7, loose: different enough that you should pick on purpose. Ink Skin is noticeably darker, cooler than Burnt Umber.

Can I use Ink Skin instead of Burnt Umber?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ink Skin is noticeably darker, cooler than Burnt Umber.

Can I use Burnt Umber instead of Ink Skin?

The same difference applies the other way round: Burnt Umber is noticeably lighter, 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.