I don't know how to describe. Please see below two images. The top image is fitted to screen with strange color casting. This problem also occurs with "fill" selected. However, it is back to normal if the image is set "1:1"
This looks like either a video driver issue or a bad display profile.
First check with your video card manufacturer to see if there is an updated driver for your system. If so, download and install and see if you still have the issue. If so, do you calibrate your monitor? If so, you may have a wonky calibration. Recalibrate your system.