Safety Orange vs Heartfire

How close are they?

ΔE 18.8, loose: different enough that you should pick on purpose. Heartfire is a little lighter, cooler than Safety Orange.

Can I use Heartfire instead of Safety Orange?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Heartfire is a little lighter, cooler than Safety Orange.

Can I use Safety Orange instead of Heartfire?

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