Naples Yellow Deep vs Leather Brown

How close are they?

ΔE 18.5, loose: different enough that you should pick on purpose. Leather Brown is noticeably darker, much more muted than Naples Yellow Deep.

Can I use Leather Brown instead of Naples Yellow Deep?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Leather Brown is noticeably darker, much more muted than Naples Yellow Deep.

Can I use Naples Yellow Deep instead of Leather Brown?

The same difference applies the other way round: Naples Yellow Deep is noticeably lighter, much more saturated.

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.