ΔE 20.4, loose: different enough that you should pick on purpose. Sahara Yellow is noticeably darker, much more muted than Fiendish Yellow.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Sahara Yellow is noticeably darker, much more muted than Fiendish Yellow.
The same difference applies the other way round: Fiendish Yellow is noticeably lighter, much more saturated.
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 Fiendish Yellow on the colour wheel See Sahara Yellow on the colour wheel
All matches: Fiendish Yellow equivalents · Sahara Yellow equivalents