AII Light Blue vs Celestra Grey

How close are they?

ΔE 7.9, close: similar, with a visible difference side by side. Celestra Grey is more muted than AII Light Blue.

Can I use Celestra Grey instead of AII Light Blue?

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

Can I use AII Light Blue instead of Celestra Grey?

The same difference applies the other way round: AII Light Blue is 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.