ΔE 8.8, close: similar, with a visible difference side by side. Flash Gitz Yellow is a little lighter than Sunny Yellow.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Flash Gitz Yellow is a little lighter than Sunny Yellow.
The same difference applies the other way round: Sunny Yellow is a little darker.
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 Sunny Yellow on the colour wheel See Flash Gitz Yellow on the colour wheel
All matches: Sunny Yellow equivalents · Flash Gitz Yellow equivalents