ΔE 9.1, close: similar, with a visible difference side by side. US Light Green is a little darker, more muted than Rock Grey.
Usually, if you are not matching paint already on the model. Close match (ΔE 9). US Light Green is a little darker, more muted than Rock Grey.
The same difference applies the other way round: Rock 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 Rock Grey on the colour wheel See US Light Green on the colour wheel
All matches: Rock Grey equivalents · US Light Green equivalents