My personal opinion is that the officially official boxes (Genesis, DS, 3DS, various disc based systems) are almost entirely opaque, usually black/dark gray, therefore when I get nicely fitting semi official boxes (Game Boy, NES, anything else he makes) from Shadowfox, I'll usually get dark gray or other opaque colors unless it's like a replacement Saturn longbox or something.
For me, clear cases for cartridge systems is reserved for "close enough" cases like the ugc, when I get a proper case it goes gray