ΔE 12.0, fair: the same colour family, but not a straight swap. Frost Blue is a little darker, warmer than Medium Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Frost Blue is a little darker, warmer than Medium Blue.
The same difference applies the other way round: Medium Blue 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 Medium Blue on the colour wheel See Frost Blue on the colour wheel
All matches: Medium Blue equivalents · Frost Blue equivalents