ΔE 6.3, close: similar, with a visible difference side by side. USAF Light Blue is a little darker, warmer than Field Gray.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). USAF Light Blue is a little darker, warmer than Field Gray.
The same difference applies the other way round: Field Gray is a little lighter, 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.
See Field Gray on the colour wheel See USAF Light Blue on the colour wheel
All matches: Field Gray equivalents · USAF Light Blue equivalents