Titan Violet Pale vs Mahogany Ink

How close are they?

ΔE 61.5, loose: different enough that you should pick on purpose. Mahogany Ink is noticeably darker, more saturated than Titan Violet Pale.

Can I use Mahogany Ink instead of Titan Violet Pale?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 62). Mahogany Ink is noticeably darker, more saturated than Titan Violet Pale.

Can I use Titan Violet Pale instead of Mahogany Ink?

The same difference applies the other way round: Titan Violet Pale is noticeably lighter, more muted.

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.