Safety Orange vs Orange Yellow

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Orange Yellow is a little lighter, more saturated, cooler than Safety Orange.

Can I use Orange Yellow instead of Safety Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 21). Orange Yellow is a little lighter, more saturated, cooler than Safety Orange.

Can I use Safety Orange instead of Orange Yellow?

The same difference applies the other way round: Safety Orange is a little darker, more muted, warmer.

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.