Best guess would be that the paint is reacting with whatever adhesive layer is below it -- the only sure fix is to strip the paint and repaint the entire system (it's unlikely repairing just small areas will result in a satisfactory finish).

It's most evident on the corners and creases where the paint layer is probably thinner than on the rest of the notebook, but heat could easily be a factor.

I too thought of heat could be the cause, however I really can't quite agree with this one. Because heating doesn't happen on screen chassis at all, yet most evident orange is there. If the heat was issue, entire above the keyboard would get dark orange. Right? I think there is else cause and a hidden solution with some kind of cleaning material. Might be I am being hopeful though.

Any chance this system has seen the inside of a carrying bag with an orange or red lining or orange or red stitching on it?

Hi, the bags I've used never had any orange or red lining/stitching anywhere of them.

I am really curious what would be the cause.

Whatever it is, you have two repair options:  replace the affected parts, or have the entire system stripped of paint and then have it repainted.

Thank you, I will be contacting with local Dell service. Meantime, I can wait for experiences and knowledge of users sharing.