Underhive Ash vs Light Green Grey

How close are they?

ΔE 6.7, close: similar, with a visible difference side by side. Light Green Grey is more muted than Underhive Ash.

Can I use Light Green Grey instead of Underhive Ash?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Light Green Grey is more muted than Underhive Ash.

Can I use Underhive Ash instead of Light Green Grey?

The same difference applies the other way round: Underhive Ash is 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.