Frenzy Orange vs Imperial Yellow

How close are they?

ΔE 23.4, loose: different enough that you should pick on purpose. Imperial Yellow is noticeably lighter, more muted than Frenzy Orange.

Can I use Imperial Yellow instead of Frenzy Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Imperial Yellow is noticeably lighter, more muted than Frenzy Orange.

Can I use Frenzy Orange instead of Imperial Yellow?

The same difference applies the other way round: Frenzy Orange is noticeably darker, 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.