ΔE 16.3, loose: different enough that you should pick on purpose. Grey Brown is a little lighter, much more saturated than Raw Umber.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Grey Brown is a little lighter, much more saturated than Raw Umber.
The same difference applies the other way round: Raw Umber is a little darker, much 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.
See Raw Umber on the colour wheel See Grey Brown on the colour wheel
All matches: Raw Umber equivalents · Grey Brown equivalents