Warm Yellow vs Beasty Brown

How close are they?

ΔE 9.4, close: similar, with a visible difference side by side. Beasty Brown is a little darker than Warm Yellow.

Can I use Beasty Brown instead of Warm Yellow?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Beasty Brown is a little darker than Warm Yellow.

Can I use Warm Yellow instead of Beasty Brown?

The same difference applies the other way round: Warm Yellow is a little lighter.

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.