macbook pro 15 touchbar display issues

Hi,

This concerns my one year old MBP 15" touchbar running 10.13.2. I quite suddenly noticed these yellow fairly diffuse discolourations in the corners of the display. These are intermittent and may affect all corners, but in a variable pattern and slowly changing over time, sometimes appearing lefthand bottom corner, sometimes right hand. It is not on the surface of the display nor in the actual image on the display (it does not scroll with the image). Pressing on the display with a finger seems to bleach it for want of a better description (either from the physical pressure or temperature change), see images before and after pressing screen.

In my mind clearly not a software or graphics card issue, but would appreciate any thoughts on what this could be.

Many thanks

Jan