ΔE 13.8, fair: the same colour family, but not a straight swap. Ultramarine Highlight is a little lighter, more saturated, warmer than Thousand Sons Blue.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 14). Ultramarine Highlight is a little lighter, more saturated, warmer than Thousand Sons Blue.
The same difference applies the other way round: Thousand Sons Blue is a little darker, more muted, cooler.
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 Thousand Sons Blue on the colour wheel See Ultramarine Highlight on the colour wheel
All matches: Thousand Sons Blue equivalents · Ultramarine Highlight equivalents