Catachan Flesh vs English Field Brown

How close are they?

ΔE 17.1, loose: different enough that you should pick on purpose. English Field Brown is a little darker, much more saturated than Catachan Flesh.

Can I use English Field Brown instead of Catachan Flesh?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). English Field Brown is a little darker, much more saturated than Catachan Flesh.

Can I use Catachan Flesh instead of English Field Brown?

The same difference applies the other way round: Catachan Flesh is a little lighter, much 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.