Before you had a white chart while using a dark theme, which was not what the user expects. This was changed when themes were added to charts in https://github.com/eclipse/smarthome/pull/4291. The client side change to request those themes was https://github.com/openhab/openhab-android/pull/386.
In the latest beta (2.1.9) there is a setting to change the chart scaling.
The solution ? Conclusion? it is solved?
I´m on snapshots and yes, now it works. You can configure charts in paper ui and inside habdroid (openhab android app).