ΔE 6.4, close: similar, with a visible difference side by side. Moon Yellow is a little darker than Flat Yellow.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Moon Yellow is a little darker than Flat Yellow.
The same difference applies the other way round: Flat Yellow is a little lighter.
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 Flat Yellow on the colour wheel See Moon Yellow on the colour wheel
All matches: Flat Yellow equivalents · Moon Yellow equivalents