Deep Grey vs Mage Hunter Green

How close are they?

ΔE 21.0, loose: different enough that you should pick on purpose. Mage Hunter Green is more saturated, warmer than Deep Grey.

Can I use Mage Hunter Green instead of Deep Grey?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Mage Hunter Green is more saturated, warmer than Deep Grey.

Can I use Deep Grey instead of Mage Hunter Green?

The same difference applies the other way round: Deep Grey is 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.