Blood Red vs Cardinal Purple

How close are they?

ΔE 22.4, loose: different enough that you should pick on purpose. Cardinal Purple is a little darker, more muted, cooler than Blood Red.

Can I use Cardinal Purple instead of Blood Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Cardinal Purple is a little darker, more muted, cooler than Blood Red.

Can I use Blood Red instead of Cardinal Purple?

The same difference applies the other way round: Blood Red is a little lighter, 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.