ΔE 15.1, loose: different enough that you should pick on purpose. Mud Brown is noticeably lighter, more muted than Agrax Earthshade. They are different kinds of paint: Citadel Agrax Earthshade is a wash/shade and Nocturna Models Mud Brown is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Mud Brown is noticeably lighter, more muted than Agrax Earthshade. They are different kinds of paint.
The same difference applies the other way round: Agrax Earthshade is noticeably darker, more saturated.
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.
See Agrax Earthshade on the colour wheel See Mud Brown on the colour wheel
All matches: Agrax Earthshade equivalents · Mud Brown equivalents