Spectral Blue vs Medium Grey Blue

How close are they?

ΔE 9.0, close: similar, with a visible difference side by side. Medium Grey Blue is more muted, warmer than Spectral Blue.

Can I use Medium Grey Blue instead of Spectral Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Medium Grey Blue is more muted, warmer than Spectral Blue.

Can I use Spectral Blue instead of Medium Grey Blue?

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

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.