Medieval Forest vs Grey Green

How close are they?

ΔE 17.6, loose: different enough that you should pick on purpose. Grey Green is a little lighter, much more muted, warmer than Medieval Forest.

Can I use Grey Green instead of Medieval Forest?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Grey Green is a little lighter, much more muted, warmer than Medieval Forest.

Can I use Medieval Forest instead of Grey Green?

The same difference applies the other way round: Medieval Forest is a little darker, 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.