WWI German Red Brown vs Martian Ironearth

How close are they?

ΔE 11.7, fair: the same colour family, but not a straight swap. Martian Ironearth is noticeably lighter, more saturated than WWI German Red Brown. They are different kinds of paint: AK Interactive WWI German Red Brown is an opaque base/layer paint and Citadel Martian Ironearth is a technical paint or medium, so they won’t behave the same on the model even where the colour is close.

Can I use Martian Ironearth instead of WWI German Red Brown?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Martian Ironearth is noticeably lighter, more saturated than WWI German Red Brown. They are different kinds of paint.

Can I use WWI German Red Brown instead of Martian Ironearth?

The same difference applies the other way round: WWI German Red Brown is noticeably darker, more muted.

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.