[ubuntu-uk] colour changes with vertical scroll

[Norman Silverstone]

Vertical scrolling causes the colour of whatever is on the screen to 
change and the colour returns to the original as soon as scrolling 
stops. For example, in the case of text, the colour changes from black 
to blue and back to black. I would like to troubleshoot and, if 
possible, cure this phenomenon. Google has not been particularly helpful 
and I would be grateful for any positive ideas and things to do. Thanks 
in advance.

Norman