The answer given in the book is that, as it turns out, they have color receptors in their skin. The book notes that this is only a partial answer, because they still only have one color receptor in their skin, which still doesn’t allow for color vision, so this doesn’t fully solve the puzzle, but Godfrey-Smith speculates that perhaps the combination of one color receptor with color-changing cells in front of the color receptor allows them to gain some information about the color of things around it (121-123).
The answer given in the book is that, as it turns out, they have color receptors in their skin. The book notes that this is only a partial answer, because they still only have one color receptor in their skin, which still doesn’t allow for color vision, so this doesn’t fully solve the puzzle, but Godfrey-Smith speculates that perhaps the combination of one color receptor with color-changing cells in front of the color receptor allows them to gain some information about the color of things around it (121-123).