Runelord Brass vs Martian Green

How close are they?

ΔE 30.5, loose: different enough that you should pick on purpose. Martian Green is a little darker, more muted, cooler than Runelord Brass.

Can I use Martian Green instead of Runelord Brass?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 31). Martian Green is a little darker, more muted, cooler than Runelord Brass.

Can I use Runelord Brass instead of Martian Green?

The same difference applies the other way round: Runelord Brass is a little lighter, more saturated, warmer.

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.