Dark Marine Green vs Greenskin

How close are they?

ΔE 6.0, close: similar, with a visible difference side by side. Greenskin is a little lighter than Dark Marine Green.

Can I use Greenskin instead of Dark Marine Green?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Greenskin is a little lighter than Dark Marine Green.

Can I use Dark Marine Green instead of Greenskin?

The same difference applies the other way round: Dark Marine Green is a little darker.

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.