Desert Yellow vs Cokum Copper

How close are they?

ΔE 15.1, loose: different enough that you should pick on purpose. Cokum Copper is a little lighter, much more saturated, warmer than Desert Yellow.

Can I use Cokum Copper instead of Desert Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Cokum Copper is a little lighter, much more saturated, warmer than Desert Yellow.

Can I use Desert Yellow instead of Cokum Copper?

The same difference applies the other way round: Desert Yellow is a little darker, much more muted, 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.