Color of the custom statistics data trend using the XML file gets overwritten when there is a UI change on the statistics tab

I created some custom charts, but when I modify the color of the graph using the XML file it gets overwritten whenever there is a change in the UI on the statistics tab, for example if i make a new chart or add a new data set and click save using the interface on the statistics tab. Is this supposed to happen, or is there some other way to modify the colors? It would be great if i could select the color when i select which data tag to use for creating the custom chart, but i don't think that is currently an option.