ΔE 6.7, close: similar, with a visible difference side by side. Thicket Grove is a little lighter, warmer than Rock Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 7). Thicket Grove is a little lighter, warmer than Rock Grey.
The same difference applies the other way round: Rock Grey is a little darker, 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 Rock Grey on the colour wheel See Thicket Grove on the colour wheel
All matches: Rock Grey equivalents · Thicket Grove equivalents