Hello,
I have found a bug in the style tab of a chart configuration. And it is that when a chart has been created, and you access to its configuration to enable a title, it does not allow to modify the color (the forbidden symbol appears when you try to click to change it). The solution I have found is to enable and disable the title consecutively. I have tested in both versions 8.0.9 and 7.4.9 and the bug appears in both versions.
Thank you!