Pink Horror vs Red Purple

How close are they?

ΔE 9.9, close: similar, with a visible difference side by side. Red Purple is a little darker, more saturated, warmer than Pink Horror.

Can I use Red Purple instead of Pink Horror?

Usually, if you are not matching paint already on the model. Close match (ΔE 10). Red Purple is a little darker, more saturated, warmer than Pink Horror.

Can I use Pink Horror instead of Red Purple?

The same difference applies the other way round: Pink Horror is a little lighter, 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.