Imp Yellow vs Golden Griffon

How close are they?

ΔE 18.6, loose: different enough that you should pick on purpose. Golden Griffon is noticeably darker, much more saturated than Imp Yellow.

Can I use Golden Griffon instead of Imp Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Golden Griffon is noticeably darker, much more saturated than Imp Yellow.

Can I use Imp Yellow instead of Golden Griffon?

The same difference applies the other way round: Imp Yellow is noticeably lighter, much 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.