Ruddy Fur vs Darkoath Flesh

How close are they?

ΔE 17.5, loose: different enough that you should pick on purpose. Darkoath Flesh is a little lighter, much more muted, cooler than Ruddy Fur.

Can I use Darkoath Flesh instead of Ruddy Fur?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Darkoath Flesh is a little lighter, much more muted, cooler than Ruddy Fur.

Can I use Ruddy Fur instead of Darkoath Flesh?

The same difference applies the other way round: Ruddy Fur is a little darker, much more saturated, 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.