Moldy Wine vs Hastur Purple

How close are they?

ΔE 7.1, close: similar, with a visible difference side by side. Hastur Purple is a little darker, warmer than Moldy Wine.

Can I use Hastur Purple instead of Moldy Wine?

Usually, if you are not matching paint already on the model. Close match (ΔE 7). Hastur Purple is a little darker, warmer than Moldy Wine.

Can I use Moldy Wine instead of Hastur Purple?

The same difference applies the other way round: Moldy Wine is a little lighter, 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.