ΔE 32.6, loose: different enough that you should pick on purpose. Sky Grey is noticeably lighter, much more muted than Aegis Aqua.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 33). Sky Grey is noticeably lighter, much more muted than Aegis Aqua.
The same difference applies the other way round: Aegis Aqua 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.
See Aegis Aqua on the colour wheel See Sky Grey on the colour wheel
All matches: Aegis Aqua equivalents · Sky Grey equivalents