ΔE 10.9, fair: the same colour family, but not a straight swap. Oxford Blue is a little darker, more saturated, warmer than Blue Mountain.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Oxford Blue is a little darker, more saturated, warmer than Blue Mountain.
The same difference applies the other way round: Blue Mountain is a little lighter, more muted, 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 Blue Mountain on the colour wheel See Oxford Blue on the colour wheel
All matches: Blue Mountain equivalents · Oxford Blue equivalents