Zealot Yellow vs Orange

How close are they?

ΔE 42.8, loose: different enough that you should pick on purpose. Orange is noticeably darker, warmer than Zealot Yellow.

Can I use Orange instead of Zealot Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 43). Orange is noticeably darker, warmer than Zealot Yellow.

Can I use Zealot Yellow instead of Orange?

The same difference applies the other way round: Zealot Yellow is noticeably lighter, cooler.

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.