1. In the custom control, go to the All Properties of the viewpanel > look for 'data (var)' property > give it a value (say 'ventry')
2. Go to the All Properties of the 'total' column > look for 'styling (style)' property > compute the following code into it:
if(ventry.isCategory()||ventry.isTotal())
"color:rgb(0,0,255)";
I select (0,0,255) which is blue for example. Change to whatever color you want. Also, I only test in Notes Client browser. Not sure if it'll work on others.