ΔE 16.7, loose: different enough that you should pick on purpose. Grey Mist is a little lighter, more muted than Burnt Moss.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Grey Mist is a little lighter, more muted than Burnt Moss.
The same difference applies the other way round: Burnt Moss is a little 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 Burnt Moss on the colour wheel See Grey Mist on the colour wheel
All matches: Burnt Moss equivalents · Grey Mist equivalents