ΔE 12.2, fair: the same colour family, but not a straight swap. Light Emerald is a little lighter, more muted, cooler than Majestic Fortress.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Light Emerald is a little lighter, more muted, cooler than Majestic Fortress.
The same difference applies the other way round: Majestic Fortress is a little darker, more saturated, warmer.
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 Majestic Fortress on the colour wheel See Light Emerald on the colour wheel
All matches: Majestic Fortress equivalents · Light Emerald equivalents