Terrestrial Titan vs Gravedigger Denim

How close are they?

ΔE 16.6, loose: different enough that you should pick on purpose. Gravedigger Denim is a little lighter, more muted than Terrestrial Titan.

Can I use Gravedigger Denim instead of Terrestrial Titan?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 17). Gravedigger Denim is a little lighter, more muted than Terrestrial Titan.

Can I use Terrestrial Titan instead of Gravedigger Denim?

The same difference applies the other way round: Terrestrial Titan 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.