Brown Tone vs Mortarion Grime

How close are they?

ΔE 24.8, loose: different enough that you should pick on purpose. Mortarion Grime is noticeably lighter, more muted, cooler than Brown Tone.

Can I use Mortarion Grime instead of Brown Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Mortarion Grime is noticeably lighter, more muted, cooler than Brown Tone.

Can I use Brown Tone instead of Mortarion Grime?

The same difference applies the other way round: Brown Tone is noticeably darker, 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.