iMac retina 5k 27" late 2015 pink tint around the display edge.

Hi,

Thanks for participating in Apple Support Communities. We see from your screenshot that you're seeing this pink tint around the sides of your display. We'd like to help.

Does this happen on each screen/app you're using? Does it return after you restart your iMac?

The following resource can help you troubleshoot this issue:

If your Mac display doesn’t look right

Hope that helps!

Hi,

Thanks for keeping us updated on the steps you completed with your iMac.

From here, it sounds like the best next step would be to have your iMac evaluated for service. Depending on your region, that can be done at a local Apple Authorized Service Provider or Apple Store or through a mail-in process. Find Locations in your area to see if that would work for you. Then, Contact Apple Support if you want to look at possible mail-in options or have any other questions about this process. 

Hope that helps!