How to change the background color of a graph for one chart and the default value.
You can set the background color of an individual chart via the UI. Click on the icon Additional Chartig Options (4th icon from the left) > Borders and Colors tab > Background Color.
However you cannot set charts' background color globally.
Some Corda parms have been externalized to XML files in the style directory \OracleBI\web\app\res\s_oracle10, and you can change the default color for the actual chart in the palette.cxml file by changing the order of the colors but you cannot set charts' background color globally.