ΔE 9.6, close: similar, with a visible difference side by side. Gravestone Blue is a little darker, more muted, cooler than Runic Cobalt.
Usually, if you are not matching paint already on the model. Close match (ΔE 10). Gravestone Blue is a little darker, more muted, cooler than Runic Cobalt.
The same difference applies the other way round: Runic Cobalt is a little lighter, 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 Runic Cobalt on the colour wheel See Gravestone Blue on the colour wheel
All matches: Runic Cobalt equivalents · Gravestone Blue equivalents