Orange Magma vs Ochre Desert

How close are they?

ΔE 15.9, loose: different enough that you should pick on purpose. Ochre Desert is noticeably darker, more saturated than Orange Magma.

Can I use Ochre Desert instead of Orange Magma?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Ochre Desert is noticeably darker, more saturated than Orange Magma.

Can I use Orange Magma instead of Ochre Desert?

The same difference applies the other way round: Orange Magma is noticeably lighter, more muted.

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.