Black Templar vs Greasy Black

How close are they?

ΔE 8.6, close: similar, with a visible difference side by side. Greasy Black is a little lighter than Black Templar.

Can I use Greasy Black instead of Black Templar?

Usually, if you are not matching paint already on the model. Close match (ΔE 9). Greasy Black is a little lighter than Black Templar.

Can I use Black Templar instead of Greasy Black?

The same difference applies the other way round: Black Templar is a little darker.

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.