Penny plain / penny coloured
The price of the comic was a halfpenny for an uncoloured one, a penny if it was coloured.
A penny plain and twopence coloured was a well-known phrase in the 19th century. I don't know whether Robert Louis Stevenson originated it, but he used it as the title of an essay about the toy theatres (using paper cut-out figures) that he had played with as a boy. The child could either colour in their own figures or buy them ready-coloured.