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