As I'm experimenting with customizing Budgie experience, I found out a functionality that actually could help me: Stylize Regions. Does someone here know what is actually for and how to handle it?

As the description says, it adds a hint of darker shade to differentiate different portions of the taskbar from each other. It isn't as visible with certain themes or options. Here is an unlisted clip (not mine) which demonstrates it if you're curious.