Ulthuan Grey vs Ion Blue

How close are they?

ΔE 8.3, close: similar, with a visible difference side by side. Ion Blue is a little lighter, more saturated than Ulthuan Grey.

Can I use Ion Blue instead of Ulthuan Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Ion Blue is a little lighter, more saturated than Ulthuan Grey.

Can I use Ulthuan Grey instead of Ion Blue?

The same difference applies the other way round: Ulthuan Grey is a little darker, 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.