Yellow Green vs Buff

How close are they?

ΔE 20.0, loose: different enough that you should pick on purpose. Buff is a little darker, more muted, warmer than Yellow Green.

Can I use Buff instead of Yellow Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Buff is a little darker, more muted, warmer than Yellow Green.

Can I use Yellow Green instead of Buff?

The same difference applies the other way round: Yellow Green 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.