Selecting a chart, colors disappear.
 

This doesn't happen all of the time and I should mention that it relates to
charts graphing real-time data in case that is an issue, but occasionally
when I select a chart where the black squares appear on corners and
mid-points, the normal colors on the chart all suddenly go to black, that
is, the chart appears to be in black and white, not color. After I finish
whatever task I was doing and deselect the chart, the colors all re-appear.

No damage or anything, but I am curious what causes it and why it is
intermittent.

My thanks in advance for any ideas.

Brad