ΔE 8.3, close: similar, with a visible difference side by side. Sand Beige is a little darker, cooler than Buff.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Sand Beige is a little darker, cooler than Buff.
The same difference applies the other way round: Buff is a little lighter, warmer.
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 Buff on the colour wheel See Sand Beige on the colour wheel
All matches: Buff equivalents · Sand Beige equivalents