Zealot Yellow vs Radiant Orange

How close are they?

ΔE 54.7, loose: different enough that you should pick on purpose. Radiant Orange is noticeably darker, much more muted, warmer than Zealot Yellow.

Can I use Radiant Orange instead of Zealot Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 55). Radiant Orange is noticeably darker, much more muted, warmer than Zealot Yellow.

Can I use Zealot Yellow instead of Radiant Orange?

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