Medium Grey vs USAF Light Gray

How close are they?

ΔE 7.0, close: similar, with a visible difference side by side. USAF Light Gray is a little lighter, more saturated than Medium Grey.

Can I use USAF Light Gray instead of Medium Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). USAF Light Gray is a little lighter, more saturated than Medium Grey.

Can I use Medium Grey instead of USAF Light Gray?

The same difference applies the other way round: Medium 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.