Slaughter Red vs Red Opulence

How close are they?

ΔE 22.7, loose: different enough that you should pick on purpose. Red Opulence is noticeably lighter, much more saturated, warmer than Slaughter Red.

Can I use Red Opulence instead of Slaughter Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Red Opulence is noticeably lighter, much more saturated, warmer than Slaughter Red.

Can I use Slaughter Red instead of Red Opulence?

The same difference applies the other way round: Slaughter Red is noticeably darker, much 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.