ΔE 6.3, close: similar, with a visible difference side by side. Payne's Gray is more saturated, warmer than Night Sky. They are different kinds of paint: Army Painter Night Sky is an opaque base/layer paint and Golden Payne's Gray is an ink, glaze or transparent paint, so they won’t behave the same on the model even where the colour is close.
Usually, if you are not matching paint already on the model. Close match (ΔE 6). Payne's Gray is more saturated, warmer than Night Sky. They are different kinds of paint.
The same difference applies the other way round: Night Sky is more muted, cooler.
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 Night Sky on the colour wheel See Payne's Gray on the colour wheel
All matches: Night Sky equivalents · Payne's Gray equivalents