IJA Grey Green vs Longbeard Grey

How close are they?

ΔE 6.1, close: similar, with a visible difference side by side. Longbeard Grey is a little lighter than IJA Grey Green.

Can I use Longbeard Grey instead of IJA Grey Green?

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

Can I use IJA Grey Green instead of Longbeard Grey?

The same difference applies the other way round: IJA Grey 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.