ΔE 15.4, loose: different enough that you should pick on purpose. Sky Blue is noticeably lighter, more muted than Crystal Blue.
✓ Herrick Games paint comparison chart lists these two as equivalents.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Sky Blue is noticeably lighter, more muted than Crystal Blue.
The same difference applies the other way round: Crystal Blue 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.
See Crystal Blue on the colour wheel See Sky Blue on the colour wheel
All matches: Crystal Blue equivalents · Sky Blue equivalents