Light Gull Grey FS 16440 vs Underhive Ash

How close are they?

ΔE 8.2, close: similar, with a visible difference side by side. Underhive Ash is more saturated than Light Gull Grey FS 16440.

Can I use Underhive Ash instead of Light Gull Grey FS 16440?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Underhive Ash is more saturated than Light Gull Grey FS 16440.

Can I use Light Gull Grey FS 16440 instead of Underhive Ash?

The same difference applies the other way round: Light Gull Grey FS 16440 is more muted.

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.