Longbeard Grey vs Moonstone Grey

How close are they?

ΔE 8.1, close: similar, with a visible difference side by side. Moonstone Grey is a little darker, more muted than Longbeard Grey.

Can I use Moonstone Grey instead of Longbeard Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Moonstone Grey is a little darker, more muted than Longbeard Grey.

Can I use Longbeard Grey instead of Moonstone Grey?

The same difference applies the other way round: Longbeard 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.