Never mind the below! Deselecting "Automatically adjust brightness" makes this go away, in System Preferences, Displays. Back to normal :)
Thanks for the picture. Unfortunately this appears not to fix things. I tried both reset colors and reset settings. Iris crashed on reset settings. This is a new computer and I thought all settings are default so not sure if this could be a general problem. I attach a photo of my screen in case anyone else has this. Note the teal mouse and text. And the purple spots.