ΔE 18.3, loose: different enough that you should pick on purpose. Celestial Violet is noticeably lighter, cooler than Shell Shocked.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 18). Celestial Violet is noticeably lighter, cooler than Shell Shocked.
The same difference applies the other way round: Shell Shocked is noticeably darker, warmer.
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 Shell Shocked on the colour wheel See Celestial Violet on the colour wheel
All matches: Shell Shocked equivalents · Celestial Violet equivalents