Changing default colour of bar graphs on Forms - Accessibility

Hi all,

I was wondering if anyone knew how to change the default colours in the bar graphs on Forms? I've attached an image of the results from one Forms survey however it's difficult for us to be able to see the off white colour which is some of our most valuable data. This is proving very difficult for those with visual impairments and getting people on board with Forms. If I could change the colours so they would be easy to differentiate then that would be ideal.

Thanks for any help!

Kat