Bogey Green vs Undead Flesh

How close are they?

ΔE 19.4, loose: different enough that you should pick on purpose. Undead Flesh is much more muted, warmer than Bogey Green.

Can I use Undead Flesh instead of Bogey Green?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Undead Flesh is much more muted, warmer than Bogey Green.

Can I use Bogey Green instead of Undead Flesh?

The same difference applies the other way round: Bogey Green is much more saturated, 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.