Profile discoloration in Rehau Softline

Hello forum experts, I hope you can help me. During our house construction in 2009/2010, we chose Rehau Softline Brilliant Design profiles (golden oak / white). The white profile sides (i.e., inside) have discolored. It looks as if someone rolled a gray roller exactly over the profiles. Next to it remains a white edge that could have been drawn with a ruler. We can observe this on all windows. For better illustration, I am attaching a photo. I wanted to first know your opinion before my window installer tells me anything. We are, of course, a smoke-free household (also without a stove, etc.). I am eagerly waiting for your feedback!

Take a picture with a greater distance.

I'll do it later then.

Adhesive residue from the protective film? Can't get the haze off at all?

I can't get a better picture that easily. : The thing with the protective film could of course be possible. But we removed it shortly after installation. And the windows are cleaned thoroughly every 4-5 weeks. Do you know if the haze occurs more often? What can I do about it?

It's just a guess - what do you use to clean them? Do you have isopropanol? Slightly moisten a cloth and rub in one spot...