Colour Issue

I have just been reworking some old images and have found that skies which look blue in the viewer have a severe green cast in the thumbnail in the browser and it is the colour in the browser which shows on the larger image which appears when I click Export and again in the exported TIFF viewed in the old Windows Photo Viewer app, which has always given me accurate colours in the past.  I've never seen anything like this before.  I can't imagine how/why this can be happening.  I would have expected consistency of colour within Capture One, if not necessarily between Capture One and the apps used to view exported images.