Khorne Red vs Hull Red

How close are they?

ΔE 15.5, loose: different enough that you should pick on purpose. Hull Red is a little lighter, much more muted than Khorne Red.

Can I use Hull Red instead of Khorne Red?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Hull Red is a little lighter, much more muted than Khorne Red.

Can I use Khorne Red instead of Hull Red?

The same difference applies the other way round: Khorne Red is a little darker, much more saturated.

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.