Maybe glaucus would have been it.You do have to wonder what word they would have used to describe a light-blue shade. Would caeruleus have worked? Caeruleus seems to have been rather about dark shades, be they blue or green or downright black.
I would like to find that passage as well...If the passage exists I suspect the word might have been glaucus, which is blue-gray... or... gray-green.