ΔE 13.8, fair: the same colour family, but not a straight swap. IDF Blue is a little lighter, much more muted than Flat Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). IDF Blue is a little lighter, much more muted than Flat Blue.
The same difference applies the other way round: Flat Blue is a little darker, much 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.
See Flat Blue on the colour wheel See IDF Blue on the colour wheel
All matches: Flat Blue equivalents · IDF Blue equivalents