Yea, I think tilmoore69 is right. You want paint for the hard vinyl kickpanels, not dye, as indicated in the description for the CJPony product he/she cited.
For whatever it's worth, I put plastic eve vents in my house at least 10 years ago. Their wrappers had in big bold letters, NOT PAINTABLE. I sprayed them with Fusion, a color close to the house trim color, then painted them with the trim color latex paint. Worked like a charm, and they still look great.