Zealot Yellow vs Nuclear Yellow

How close are they?

ΔE 28.8, loose: different enough that you should pick on purpose. Nuclear Yellow is noticeably darker, much more muted, warmer than Zealot Yellow.

Can I use Nuclear Yellow instead of Zealot Yellow?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 29). Nuclear Yellow is noticeably darker, much more muted, warmer than Zealot Yellow.

Can I use Zealot Yellow instead of Nuclear Yellow?

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.