Dark Umber vs Dark Rust

How close are they?

ΔE 14.5, fair: the same colour family, but not a straight swap. Dark Rust is more muted, cooler than Dark Umber.

Can I use Dark Rust instead of Dark Umber?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Dark Rust is more muted, cooler than Dark Umber.

Can I use Dark Umber instead of Dark Rust?

The same difference applies the other way round: Dark Umber is 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.