Titan Violet Pale vs Ink Green

How close are they?

ΔE 70.8, loose: different enough that you should pick on purpose. Ink Green is noticeably darker, much more saturated than Titan Violet Pale.

Can I use Ink Green instead of Titan Violet Pale?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 71). Ink Green is noticeably darker, much more saturated than Titan Violet Pale.

Can I use Titan Violet Pale instead of Ink Green?

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