since the stain is so light it might just be a stain from when the processor was manufactured and wasn't cleaned probably before being packaged or just a manufacturing defect stain of the lid.
It doesn't look like a burnt or overheated type stain so it should work as advertised.
You can open a AMD SUPPORT - Warranty ticket and upload your photo and see what they suggest. But I have a feeling they will say it isn't anything serious. No harm is trying though from here: https://www.amd.com/en/forms/contact-us/support.html