IJN J3 SP (Amber Grey) vs Underhive Ash

How close are they?

ΔE 9.5, close: similar, with a visible difference side by side. Underhive Ash is a little lighter, cooler than IJN J3 SP (Amber Grey).

Can I use Underhive Ash instead of IJN J3 SP (Amber Grey)?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Underhive Ash is a little lighter, cooler than IJN J3 SP (Amber Grey).

Can I use IJN J3 SP (Amber Grey) instead of Underhive Ash?

The same difference applies the other way round: IJN J3 SP (Amber Grey) is a little darker, warmer.

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.