ΔE 11.9, fair: the same colour family, but not a straight swap. Ultramarine Blue is a little lighter, more muted, cooler than Pearl Light Blue. They are different kinds of paint: Tamiya Pearl Light Blue is a pearl paint and Vallejo Ultramarine Blue is a metallic, so they won’t behave the same on the model even where the colour is close.
Only where an exact match doesn’t matter, such as a new unit or a highlight. Fair match (ΔE 12). Ultramarine Blue is a little lighter, more muted, cooler than Pearl Light Blue. They are different kinds of paint.
The same difference applies the other way round: Pearl Light Blue is a little darker, more saturated, 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 Pearl Light Blue on the colour wheel See Ultramarine Blue on the colour wheel
All matches: Pearl Light Blue equivalents · Ultramarine Blue equivalents