No clue about making one but heres two other ideas.
Get a black seat cover (probably the easiest)
or really hard: buy some sort of purple seat from K1 if they make them
That’d be what I would do! Purple is a pretty outrageous color, and with a green seatcover!.. I’d be unstoppable! I think that’s by far the best idea so far (haha, not because of barny, though)
Instead of dissecting your beautiful new green seat, maybe you could use some really really good glue to put purple fluff on. It would have to be kind of like a rug, the bottom of the purple fluff would need to be somewhat solid. That said, I think your purple theme sounds pretty cool.