ΔE 8.8, close: similar, with a visible difference side by side. Ultramarine Blue is a little darker, more saturated than Deep Cobalt Blue.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). Ultramarine Blue is a little darker, more saturated than Deep Cobalt Blue.
The same difference applies the other way round: Deep Cobalt Blue is a little lighter, more muted.
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 Deep Cobalt Blue on the colour wheel See Ultramarine Blue on the colour wheel
All matches: Deep Cobalt Blue equivalents · Ultramarine Blue equivalents