Etherium Blue vs Steel Grey

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Steel Grey is more muted, cooler than Etherium Blue.

Can I use Steel Grey instead of Etherium Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 8). Steel Grey is more muted, cooler than Etherium Blue.

Can I use Etherium Blue instead of Steel Grey?

The same difference applies the other way round: Etherium Blue is more saturated, 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.