Hi, there is a bug since ever in Xara. I thought I mention it since it hasn't been addressed in the new version either.
1) Draw a shape, click on "Create Brush" and name it "MyBrush1".
2) Draw a line, apply brush "MyBrush1", set outline color to blue, set line width to 24pt.
3) Click on "Edit Brush". In the "Fill Properties Tab" select "Local colors replace: All brush colors", increase Saturation and Hue (the brush should cycle rainbow-ish colors). Save as new brush "MyBrush2".
4) Draw a new line, apply brush "MyBrush2", set outline color to green, set line width to 24pt.
BUG: the "All brush colors"-setting has not been saved in the new brush.