ΔE 6.6, close: similar, with a visible difference side by side. Fiendish Yellow is a little darker, more saturated than Dirty Yellow.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Fiendish Yellow is a little darker, more saturated than Dirty Yellow.
The same difference applies the other way round: Dirty Yellow is a little lighter, more muted.
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 Dirty Yellow on the colour wheel See Fiendish Yellow on the colour wheel
All matches: Dirty Yellow equivalents · Fiendish Yellow equivalents