Bloodstone vs Vermilion

How close are they?

ΔE 23.2, loose: different enough that you should pick on purpose. Vermilion is a little lighter, much more saturated, cooler than Bloodstone.

Can I use Vermilion instead of Bloodstone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Vermilion is a little lighter, much more saturated, cooler than Bloodstone.

Can I use Bloodstone instead of Vermilion?

The same difference applies the other way round: Bloodstone is a little darker, much more muted, 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.