ΔE 9.8, close: similar, with a visible difference side by side. Primary Yellow is a little darker than Flash Gitz Yellow.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Primary Yellow is a little darker than Flash Gitz Yellow.
The same difference applies the other way round: Flash Gitz 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 Flash Gitz Yellow on the colour wheel See Primary Yellow on the colour wheel
All matches: Flash Gitz Yellow equivalents · Primary Yellow equivalents