ΔE 7.9, close: similar, with a visible difference side by side. Obsidian Black is a little darker, more muted than Pearl Grey. They are different kinds of paint: Scale75 Pearl Grey is a pearl paint and Vallejo Obsidian Black is a metallic, 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 8). Obsidian Black is a little darker, more muted than Pearl Grey. They are different kinds of paint.
The same difference applies the other way round: Pearl Grey is a little lighter, 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 Pearl Grey on the colour wheel See Obsidian Black on the colour wheel
All matches: Pearl Grey equivalents · Obsidian Black equivalents