Orange vs Nuclear Yellow

How close are they?

ΔE 19.5, loose: different enough that you should pick on purpose. Nuclear Yellow is more muted, warmer than Orange.

Can I use Nuclear Yellow instead of Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 20). Nuclear Yellow is more muted, warmer than Orange.

Can I use Orange instead of Nuclear Yellow?

The same difference applies the other way round: Orange is 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.