I am facing the same problème, but visual cue is not working.
I am not using variable for my bar chart colors, just the RGB finction in the background of the expression.
If I use the visual cue in the Pivot type chart, it is working for the text color (as i don't have difien colors in the bar chart) but not for the background.
I don't know how you can detect on which type of chart you are.
How did you succeed putting white as background in your pivot table?
Could you help me?