RAF Azure Blue vs Fog Grey

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Fog Grey is more muted, cooler than RAF Azure Blue.

Can I use Fog Grey instead of RAF Azure Blue?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Fog Grey is more muted, cooler than RAF Azure Blue.

Can I use RAF Azure Blue instead of Fog Grey?

The same difference applies the other way round: RAF Azure 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.