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Welcome to the Bunnings Workshop community @rmb112. It's terrific to have you join us, and many thanks for your question about painting cladding.
Warping is definitely a possibility when painting vinyl, especially if you’re considering a darker shade, so it’s important to check with the manufacturer of your cladding first. They can advise whether their product can safely be painted in a darker colour and what limitations there might be.
Aside from warping, adhesion is also a concern. Vinyl typically needs proper preparation before painting. This usually involves lightly sanding the surface to remove the sheen, then applying a primer designed for vinyl, like Dulux Max Adhesion. Standard exterior paints, such as Dulux WeatherShield, won’t adhere properly to bare vinyl without this primer.
It also matters whether your vinyl is bare or has been previously painted, as this will change the preparation process. Unfortunately, we can’t guarantee whether the cladding will warp with a darker colour. That information really needs to come from the cladding manufacturer.
Please let me know if you have any questions.
Mitchell
Hi Mitchell! Thanks for the reply and support. I'll see if can find the manufacturer details and go from there. Unfortunately, I have no information on how old or the history of the current cladding.
Thanks again! 
If you're unable to contact the manufacturer @rmb112 , the Dulux Technical team has suggested it would be best to go for a mid-tone colour, such as Dieskau, rather than a darker one.
Mitchell
