ΔE 8.7, close: similar, with a visible difference side by side. Mustard Brown is a little lighter, warmer than Russian Sand 7K.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Mustard Brown is a little lighter, warmer than Russian Sand 7K.
The same difference applies the other way round: Russian Sand 7K is a little darker, 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 Russian Sand 7K on the colour wheel See Mustard Brown on the colour wheel
All matches: Russian Sand 7K equivalents · Mustard Brown equivalents