Although all the previews are showing what appears to be the blue channel (or all colours as blue) the develop module displays the images correctly.
This has affected not only newly imported photos but the entire catalog.
disabling GPU acceleration.
Updating to the latest version of LR.
Does anyone have any ideas?
Locate the previews database (catalogname Previews.lrdata) and rename it by adding "old" in the front of the name.
Do this with Lightroom closed and restart Lightroom.