Currently Themes / Brands are not shared between Xara and Vizzlo, so in order to set your theme colors for your charts, you'll need to do this within Vizzlo. Please see their guide here on how to do this.

Likewise, after inserting a chart, if you wish to edit the colors of the chart - click on the Vizzlo icon, then hover over your chart and click edit...

This will take you into Vizzlo where you can edit your chart and colors. Once saved, you can click Update All to then update your charts within your document...