By default, the color of the chart's background is determined by the currently selected report theme. When working with Cartesian charts. segment charts, scatter plots, and gauges, this can be changed from the Background drop-down in the Component ribbon.
The background color menu is divided into 2 parts:
Theme Colors: these are the colors that have been assigned to the current report theme.
Standard Colors: these colors are available for all visualizations, regardless of the report theme.
More Colors: choose a custom Hex or RGB color; these will be displayed under a 4th section called Custom Colors.
In this example, the chart background was changed from the default color (white) to blue: