Red Tone vs Atramentum Black

How close are they?

ΔE 53.6, loose: different enough that you should pick on purpose. Atramentum Black is a little darker, much more muted than Red Tone.

Can I use Atramentum Black instead of Red Tone?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 54). Atramentum Black is a little darker, much more muted than Red Tone.

Can I use Red Tone instead of Atramentum Black?

The same difference applies the other way round: Red Tone is a little 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.