Fiendish Yellow vs Yellow FS13538

How close are they?

ΔE 10.9, fair: the same colour family, but not a straight swap. Yellow FS13538 is more saturated, warmer than Fiendish Yellow.

Can I use Yellow FS13538 instead of Fiendish Yellow?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Yellow FS13538 is more saturated, warmer than Fiendish Yellow.

Can I use Fiendish Yellow instead of Yellow FS13538?

The same difference applies the other way round: Fiendish Yellow is more muted, cooler.

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.