Deck Grey vs Longbeard Grey

How close are they?

ΔE 6.4, close: similar, with a visible difference side by side. Longbeard Grey is a little darker, more muted than Deck Grey.

Can I use Longbeard Grey instead of Deck Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Longbeard Grey is a little darker, more muted than Deck Grey.

Can I use Deck Grey instead of Longbeard Grey?

The same difference applies the other way round: Deck Grey is a little lighter, more saturated.

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.