ΔE 11.2, fair: the same colour family, but not a straight swap. Flat Yellow is a little darker, more muted than Moonbeam Yellow.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Flat Yellow is a little darker, more muted than Moonbeam Yellow.
The same difference applies the other way round: Moonbeam Yellow is a little lighter, more saturated.
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 Moonbeam Yellow on the colour wheel See Flat Yellow on the colour wheel
All matches: Moonbeam Yellow equivalents · Flat Yellow equivalents