ΔE 8.9, close: similar, with a visible difference side by side. Transparent Shading Gray is a little lighter than Regiment Grey. They are different kinds of paint: Army Painter Regiment Grey is an opaque base/layer paint and Golden Transparent Shading 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 9). Transparent Shading Gray is a little lighter than Regiment Grey. They are different kinds of paint.
The same difference applies the other way round: Regiment Grey is a little darker.
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 Regiment Grey on the colour wheel See Transparent Shading Gray on the colour wheel
All matches: Regiment Grey equivalents · Transparent Shading Gray equivalents