I used a vinyl upholstery spray inside and out to convert a tan top to black. It looked decent and held up pretty well. I did keep the car in the garage when not being driven, but it looked fine. I resprayed it after a few years and it looked better than the first time. I don't think dye would work because at least on my top the trim was vinyl anyhow....a local shop who did convertible tops suggested this little trick over a new top.....and no, I don't know where to get the spray these days.....
Jim