How to maintain colour of extruded PP beams over long term?

Hi Folks - At our workspace, we extrude beams using shredded PP and then convert them into products. We have noticed that when our beams are kept indoors, they maintain their shine and colour but when they are exposed to sun light for few days, they loose their shine and colour (attaching two contrasting pictures of our products made together about 10 months back). I know its the UV rays which play havoc but would want to know from you all, how to tackle such a problem in order to make our products outdoor friendly for a decent amount of time. Will using a thin layer of paint do the job? If yes then which type of paint might work? Any other alternatives based on your experience?

I know of no post-production, permanent solution that will not change the surface character of your product. Unlike HDPE, folks do have some success painting PP, but I have no reports from high wear circumstances where the surface is flexed during regular use. There are visually transparent, penetrating UV stabilizers for topical application- but those require at least annual renewal. Presuming low/no maintenance and minimal environmental impact are priorities, adding UV stabilizers pre-extrusion is a recourse. This might take the form of virgin material containing stabilizers, or powdered stabilizers. The least expensive and most readily available UV stabilizing additive is powdered carbon black. A bit more costly is titanium dioxide. While CB is cheaper and more effective, the plastic adopts the color of the stabilizer; just imagine sitting on a black bench mid summer. TD imparts a white cast, with marginally less protection. A Google search will produce research documents demonstrating the impact of either across a range of quantities. Of course, thoroughly mixing (or even remixing) stabilizers via extruder is going to add to your costs, and change the character of your products' appearance. A dream scenario would be to source waste plastic from a producer of outdoor furnishings or playground equipment- plastic that already includes UV stabilization. The question for me: is UV fading really a problem... or a feature? If the effects of exposure are limited to near the surface, do not significantly impact structural integrity or shedding of material on contact, then the color change could be viewed as "mellowing with time to become more harmonious with the setting". It might be worthwhile to test various colors/batches at exposure intervals to make a determination of need. (edited)