ΔE 13.8, fair: the same colour family, but not a straight swap. Dark Blue RLM24 is noticeably darker, warmer than Caspian Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Dark Blue RLM24 is noticeably darker, warmer than Caspian Blue.
The same difference applies the other way round: Caspian Blue is noticeably 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 Caspian Blue on the colour wheel See Dark Blue RLM24 on the colour wheel
All matches: Caspian Blue equivalents · Dark Blue RLM24 equivalents