ΔE 6.4, close: similar, with a visible difference side by side. Raw Umber is a little darker than Grimdark Shadow. They are different kinds of paint: Army Painter Grimdark Shadow is a wash/shade and Golden Raw Umber is an opaque base/layer 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). Raw Umber is a little darker than Grimdark Shadow. They are different kinds of paint.
The same difference applies the other way round: Grimdark Shadow is a little lighter.
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 Grimdark Shadow on the colour wheel See Raw Umber on the colour wheel
All matches: Grimdark Shadow equivalents · Raw Umber equivalents