Knitting

It's a carry over from the textile industry, where one pattern of fabric will be printed use a variety of different sets of color. Each set is a colorway. It doesn't make much sense to use colorway when talking about a solid color, but for variegated colors of sweaters with colorwork using colorway is a shorthand for listing out all the colors used, generally by using the most dominant color. A sweater that is predominantly shades of brown but also has melon and turquoise would be one with a brown colorway for instance.