Check you havnt applied an assembly level colour
Doesn't seems to be a video problems. Make sure you didn't applied any appearances to the part.
Greg and Deepak,
thanks for your suggestions.
I have not knowingly put any appearances on the parts or assembly, or changed colours out of the ordinary.
Other assemblies seem to be ok on my PC.
Most spookily, soon after I posted the question, the drawing started to behave itself.
I am still interested to know how it was caused.
Solidworks has applied appearances for me in the past, without any import from me at all..... may be worth a check.
If the views are green I would suspect it may be caused by the "Sustainability express" addin
I am glad things returned to some semblance of normal for you. It sounds like another unsolved mystery that some of us have run into.
When weird things happen like this, if you can somehow find out the sequence of commands you might
have used that triggered it, you may want to try running the Solidowrks RX tool found in Start>All Programs>
This file can be sent to Solidworks and more often then not they can pin point the cause.