I have a search that returns a stacked barchart. I put it in a dashboard. But, whatever I have tried to do, I can't get default colors to change. From other answers here, I think that the older FlashChart may work the way I want.
My question is, how to I get Splunk to use FlashChart?
You can specify the charting module (JSChart or FlashChart) in advanced XML. See the Advanced charting options topic in the documentation. It explains about the two charting modules and has a section on chart colors.