I have used the SEM brand of vinyl dyes. I have a 68 Coronet with a vinyl top. The color was fading away. I bought a quart of SEM vinyl dye and sprayed the vinyl top with it using a spray gun. It came out pretty good.
The vinyl dye lasted a long time. I sprayed the top in the late 90's. I just replaced the vinyl top in August of 2017. The dye still held for all those years and did not fade.