Daemonic Yellow vs Yellow FS33531

How close are they?

ΔE 22.0, loose: different enough that you should pick on purpose. Yellow FS33531 is a little darker, much more muted than Daemonic Yellow.

Can I use Yellow FS33531 instead of Daemonic Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Yellow FS33531 is a little darker, much more muted than Daemonic Yellow.

Can I use Daemonic Yellow instead of Yellow FS33531?

The same difference applies the other way round: Daemonic Yellow is a little 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.