Actually that’s very difficult! The ‘dark’ switch is an additional network in the compressor release path that alters the ‘shape’ of the compression release. It was a studio engineer in California who told me how a particular prototype compressor of mine sounded ‘dark’….. so I incorporated that compression release circuit into the SC2.2, but because the C2 is so compact, it would be extremely difficult to make the necessary mods. 
