Panel foreground color customization
The ability to change the background color of the panel is great. But the foreground/font color cannot be changed. This makes text (and symbolic icons) impossible to see in many situations. For example, in Adwaita Dark, if you set the panel color to white in Xfce Panel Preferences, the text and symbolic icons in the panel stay white and are illegible.
It would be nice if foreground was able to be set, or if it could automatically adjust based on the contrast/luminance/brightness of the background color chosen (auto adjust would be more complicated, but might be applicable to helping legibility when using panel transparency or using a background image).