ΔE 10.7, fair: the same colour family, but not a straight swap. Light Brown is a little darker, cooler than Buff.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Light Brown 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 Light Brown on the colour wheel
All matches: Buff equivalents · Light Brown equivalents