Tyran Blue vs Atramentum Black

How close are they?

ΔE 46.5, loose: different enough that you should pick on purpose. Atramentum Black is noticeably darker, much more muted than Tyran Blue.

Can I use Atramentum Black instead of Tyran Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 47). Atramentum Black is noticeably darker, much more muted than Tyran Blue.

Can I use Tyran Blue instead of Atramentum Black?

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