@Sarah Indeherberge - Looking at the Tables and Charts Help Center article, it appears that you can currently only change the color for Tables:

Someone has created a Wish List Idea that you may want to add your comments/vote to:

https://community.miro.com/wish-list-32/change-colour-of-charts-and-stacked-charts-1686

You could always create your own Idea in the Wish List category by following the guidelines here: Wish List: Everything You Need to Know. If you do create a Wish List Idea post, I would also recommend that you post a link to it back here, so that future readers of this post can quickly get to and vote for your Idea.

Thank you for your very quick reply. I placed my vote.

@Sarah Indeherberge - You’re welcome. Depending on how important this is to you, it may be possible to create a custom a web-plugin using the Miro Developer Platform to accomplish what you are looking for. You would probably want someone with a development background to review the developer platform documentation - probably more effort than its worth for this scenario, but I thought I would still point it out