Your photo seems to show some of the marks have a soft and irregular edge which might suggest smears on the anti reflective coating of the screen. It would be worth giving the screen a thorough clean as recommended in How to clean your Apple products - Apple Support and follow the Notebook link for your MacBook Air after reading the general advice. Start with a simple damp cloth...
If this doesn’t help I suggest you I start by making a screenshot picture (rather than your photo with a camera) then send the picture to be viewed on a different device (email it to your iPhone?). This will tell you whether the purple marks are in the image sent by the processor, or simply in the screen and display panel. Otherwise if you have an external display available, do the same marks appear on the external display?