Ice Storm vs Titan Violet Pale

How close are they?

ΔE 23.0, loose: different enough that you should pick on purpose. Titan Violet Pale is noticeably lighter, more muted than Ice Storm.

Can I use Titan Violet Pale instead of Ice Storm?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 23). Titan Violet Pale is noticeably lighter, more muted than Ice Storm.

Can I use Ice Storm instead of Titan Violet Pale?

The same difference applies the other way round: Ice Storm is noticeably 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.