ΔE 16.3, loose: different enough that you should pick on purpose. Sacra Purple is noticeably lighter, more muted than Shyish Purple. They are different kinds of paint: Citadel Shyish Purple is a one-coat contrast-style paint and Green Stuff World Sacra Purple is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Not as a straight swap; see the closer alternatives below. Loose match (ΔE 16). Sacra Purple is noticeably lighter, more muted than Shyish Purple. They are different kinds of paint.
The same difference applies the other way round: Shyish Purple 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 Shyish Purple on the colour wheel See Sacra Purple on the colour wheel
All matches: Shyish Purple equivalents · Sacra Purple equivalents