ΔE 14.9, fair: the same colour family, but not a straight swap. Muddy Olive is noticeably lighter, more saturated, warmer than Castellan Green.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 15). Muddy Olive is noticeably lighter, more saturated, warmer than Castellan Green.
The same difference applies the other way round: Castellan Green is noticeably darker, 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 Castellan Green on the colour wheel See Muddy Olive on the colour wheel
All matches: Castellan Green equivalents · Muddy Olive equivalents