Troglodyte Blue vs Coal Black

How close are they?

ΔE 25.3, loose: different enough that you should pick on purpose. Coal Black is noticeably darker, much more muted, warmer than Troglodyte Blue.

Can I use Coal Black instead of Troglodyte Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 25). Coal Black is noticeably darker, much more muted, warmer than Troglodyte Blue.

Can I use Troglodyte Blue instead of Coal Black?

The same difference applies the other way round: Troglodyte Blue is noticeably lighter, much more saturated, 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.