White Blue vs Sky Blue

How close are they?

ΔE 18.7, loose: different enough that you should pick on purpose. Sky Blue is noticeably darker, more saturated than White Blue.

Can I use Sky Blue instead of White Blue?

Not as a straight swap; see the closer alternatives below. Loose match (ΔE 19). Sky Blue is noticeably darker, more saturated than White Blue.

Can I use White Blue instead of Sky Blue?

The same difference applies the other way round: White Blue 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.