ΔE 8.0, close: similar, with a visible difference side by side. Deep Sky is a little lighter, cooler than Deep Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 8). Deep Sky is a little lighter, cooler than Deep Grey.
The same difference applies the other way round: Deep Grey is a little darker, 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 Deep Grey on the colour wheel See Deep Sky on the colour wheel
All matches: Deep Grey equivalents · Deep Sky equivalents