Demigod Flames vs Dark Sun Yellow

How close are they?

ΔE 16.7, loose: different enough that you should pick on purpose. Dark Sun Yellow is much more muted, cooler than Demigod Flames.

Can I use Dark Sun Yellow instead of Demigod Flames?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Dark Sun Yellow is much more muted, cooler than Demigod Flames.

Can I use Demigod Flames instead of Dark Sun Yellow?

The same difference applies the other way round: Demigod Flames is much more saturated, 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.