ΔE 10.0, fair: the same colour family, but not a straight swap. Bright Brown Grey is a little lighter, more muted, warmer than Monster Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 10). Bright Brown Grey is a little lighter, more muted, warmer than Monster Brown.
The same difference applies the other way round: Monster Brown is a little darker, more saturated, cooler.
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 Monster Brown on the colour wheel See Bright Brown Grey on the colour wheel
All matches: Monster Brown equivalents · Bright Brown Grey equivalents