ΔE 11.5, fair: the same colour family, but not a straight swap. Sun Yellow is a little lighter, cooler than Maize Yellow. They are different kinds of paint: Army Painter Maize Yellow is a one-coat contrast-style paint and Reaper Sun Yellow is an opaque base/layer paint, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Sun Yellow is a little lighter, cooler than Maize Yellow. They are different kinds of paint.
The same difference applies the other way round: Maize Yellow is a little darker, 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 Maize Yellow on the colour wheel See Sun Yellow on the colour wheel
All matches: Maize Yellow equivalents · Sun Yellow equivalents