If you want to post  your file  so others in the group can look at it, send it
direct to me (david at grugeon dot com dot au), or one of the other
moderators, not to the group and I will post it in the group files. Make
sure it does not contain any confidential information.

In principle the answer is that you would use the SelectionChange event for
the sheet to fire a macro when the cell  is clicked. It will fire every time
a new cell is collected so you would test to see if the cell was a relevant
one, then you would change the colour  for the particular range. How you
would do this would depend on how the chart  was constructed.

When providing more information, it would be helpful to say what version of
excel you are using.