ΔE 12.5, fair: the same colour family, but not a straight swap. Field Gray is a little lighter, more muted, cooler than Deep Azure.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 13). Field Gray is a little lighter, more muted, cooler than Deep Azure.
The same difference applies the other way round: Deep Azure is a little darker, 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.
See Deep Azure on the colour wheel See Field Gray on the colour wheel
All matches: Deep Azure equivalents · Field Gray equivalents