That is not normal in that it wouldn’t be made that way, but it’s normal since it’s understandable how it could happen. That is a cosmetic issue with the LCD panel. Without a physical inspection or examining the panel, my best guess is the layers are compressed physically. No need to repair it until you can’t or won’t abide by the color shift or the area just stops working.
Get a quote for how much it would cost to fix it, then consider:
- putting that cash in a jar and deciding if you’d rather save it for your next computer or an iPad or a brand new external display.
That way the money is there to unlock something you want in the future as a post to a nagging doubt that your current machine has a flaw in it. If Apple wants to cover it under warranty, r dilemma is solved so definitely get a quote for repair.
As to the coming and going, If you carry your Mac in the book bag or it could be getting otherwise squeezed, that would explain why the color moves around in the dissipates as the glass and plastic layers reset themselves. Like a thin film of oil or soap on water, you are seeing a rainbow of diffraction and refraction as the light and LCD interact with each other.