Dark Yellow vs Yellow FS33531

How close are they?

ΔE 14.1, fair: the same colour family, but not a straight swap. Yellow FS33531 is a little lighter, more saturated than Dark Yellow.

Can I use Yellow FS33531 instead of Dark Yellow?

Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Yellow FS33531 is a little lighter, more saturated than Dark Yellow.

Can I use Dark Yellow instead of Yellow FS33531?

The same difference applies the other way round: Dark Yellow is a little darker, 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.