ΔE 11.3, fair: the same colour family, but not a straight swap. Mustard Brown is a little darker, more muted, warmer than RLM 79 Sandy Brown.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Mustard Brown is a little darker, more muted, warmer than RLM 79 Sandy Brown.
The same difference applies the other way round: RLM 79 Sandy Brown is a little lighter, 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 RLM 79 Sandy Brown on the colour wheel See Mustard Brown on the colour wheel
All matches: RLM 79 Sandy Brown equivalents · Mustard Brown equivalents