Coverite's Presto can be used on plastic. I used it on an ABS cowl back in '88. I don't know if Presto is still available as I haven't seen it in about 10 years. Sig used to market the same covering under a different name, which I don't recall, as well.

If you can't find either Presto or the Sig equivalent, you can buy paints that match your covering. For Monokote, I recommend Lusterkote and for Ultracote, I recommend Ultra Paints. Their matching is very good. Perfect paints match Monokote very well. However, their Ultracote matching is less than perfect and their paints are quite expensive.

Rob