Infernal Red vs Warlord Purple

How close are they?

ΔE 21.5, loose: different enough that you should pick on purpose. Warlord Purple is a little lighter, cooler than Infernal Red.

Can I use Warlord Purple instead of Infernal Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Warlord Purple is a little lighter, cooler than Infernal Red.

Can I use Infernal Red instead of Warlord Purple?

The same difference applies the other way round: Infernal Red is a little darker, 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.