Bloodstain Red vs Dark Red

How close are they?

ΔE 6.5, close: similar, with a visible difference side by side. Dark Red is a little lighter, more muted than Bloodstain Red.

Can I use Dark Red instead of Bloodstain Red?

Usually, if you are not matching paint already on the model. Close match (ΔE 6). Dark Red is a little lighter, more muted than Bloodstain Red.

Can I use Bloodstain Red instead of Dark Red?

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