ΔE 21.7, loose: different enough that you should pick on purpose. Moonstone Grey is noticeably darker, much more muted than Blue Horror.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 22). Moonstone Grey is noticeably darker, much more muted than Blue Horror.
The same difference applies the other way round: Blue Horror is noticeably lighter, 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 Blue Horror on the colour wheel See Moonstone Grey on the colour wheel
All matches: Blue Horror equivalents · Moonstone Grey equivalents