Doomfire Magenta vs Red Opulence

How close are they?

ΔE 42.3, loose: different enough that you should pick on purpose. Red Opulence is more saturated, warmer than Doomfire Magenta.

Can I use Red Opulence instead of Doomfire Magenta?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 42). Red Opulence is more saturated, warmer than Doomfire Magenta.

Can I use Doomfire Magenta instead of Red Opulence?

The same difference applies the other way round: Doomfire Magenta is more muted, 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.