I've gone a couple rounds with sherwin williams on this issue. They have told me
- You can only paint lighter than existing
- You can paint only from the palette of vinyl colors in superpaint
- You can paint vinyl any color you want in superpaint
If you can pin them down on this one let me know. I've been thinking about this one quite a bit. I think if you go with an approved vinyl paint (like super paint or resilience) the same uv index or lower you should be fine. Early spring will be the time to do it. The temp will be low enough that the vinyl will be at it's relative smallest size and high enough to paint without the product dripping off the siding. I'm concerned that if I paint late in the season the vinyl will have been expanded and when winter rolls back around, contraction sets in and you see mad holidays.
I'm sure my compatriots will chime in with their opinions.