Matt Sky Blue vs Ink White

How close are they?

ΔE 25.7, loose: different enough that you should pick on purpose. Ink White is noticeably lighter, much more muted than Matt Sky Blue.

Can I use Ink White instead of Matt Sky Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 26). Ink White is noticeably lighter, much more muted than Matt Sky Blue.

Can I use Matt Sky Blue instead of Ink White?

The same difference applies the other way round: Matt Sky Blue is noticeably darker, 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.