Underbelly Blue vs Liquid Mask

How close are they?

ΔE 8.6, close: similar, with a visible difference side by side. Liquid Mask is a little lighter, more muted than Underbelly Blue.

Can I use Liquid Mask instead of Underbelly Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Liquid Mask is a little lighter, more muted than Underbelly Blue.

Can I use Underbelly Blue instead of Liquid Mask?

The same difference applies the other way round: Underbelly Blue is a little darker, 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.