Donkey Grey vs USAF Light Gray

How close are they?

ΔE 6.2, close: similar, with a visible difference side by side. USAF Light Gray is a little lighter than Donkey Grey.

Can I use USAF Light Gray instead of Donkey Grey?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). USAF Light Gray is a little lighter than Donkey Grey.

Can I use Donkey Grey instead of USAF Light Gray?

The same difference applies the other way round: Donkey Grey is a little darker.

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.