Thanks for the responses. I guess I have a few options. After I posted this question and turned the computer off for the night, I had a thought, because they are not a custom order as such (at anytime, I could have a few pairs of each colour already made), so my listing could reflect that I have say six units available and just get the buyer to convo me with their colour choice.
Of course, I might just stick with separate listings for each colour.
Might have to think on it a little before I list.