Commando Green vs Dark Reaper

How close are they?

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

Can I use Dark Reaper instead of Commando Green?

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

Can I use Commando Green instead of Dark Reaper?

The same difference applies the other way round: Commando 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.