ΔE 15.1, loose: different enough that you should pick on purpose. Deep Sky Blue is noticeably lighter, warmer than Medium Blue.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 15). Deep Sky Blue is noticeably lighter, warmer than Medium Blue.
The same difference applies the other way round: Medium Blue is noticeably darker, cooler.
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 Medium Blue on the colour wheel See Deep Sky Blue on the colour wheel
All matches: Medium Blue equivalents · Deep Sky Blue equivalents