Pyrrhic Dawn vs Sunset Orange

How close are they?

ΔE 19.3, loose: different enough that you should pick on purpose. Sunset Orange is noticeably darker, much more saturated than Pyrrhic Dawn.

Can I use Sunset Orange instead of Pyrrhic Dawn?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Sunset Orange is noticeably darker, much more saturated than Pyrrhic Dawn.

Can I use Pyrrhic Dawn instead of Sunset Orange?

The same difference applies the other way round: Pyrrhic Dawn is noticeably lighter, much more muted.

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.