I assume you are a private individual with a single dwelling in the UK in mind: This is unlikely to be available unless as a "custom" order. PVC is produced in pellet or granular form, then gently heated and extruded under slight pressure. The different profiles are made by extruding through different dies/nozzles. In practice the process is no different if different colours are involved, it simply requires a different batch of granules. However, to the best of my knowledge none of the profiles are made in the UK so you would need to order from abroad and to change to your desired colour you would need to pay for a special run - something that is almost certainly prohibitively expensive unless for example for a large commercial building. I imagine this has been and will be done but your best chance would be to tag onto someone else's run and accept their colour. You would need to establish contact with a manufacturer, almost certainly in Germany - you could go through a distributor in the UK.