ΔE 11.2, fair: the same colour family, but not a straight swap. Ultramarine Shadow is a little darker, more muted than Shadow Thorn.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 11). Ultramarine Shadow is a little darker, more muted than Shadow Thorn.
The same difference applies the other way round: Shadow Thorn is a little lighter, 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 Shadow Thorn on the colour wheel See Ultramarine Shadow on the colour wheel
All matches: Shadow Thorn equivalents · Ultramarine Shadow equivalents