Design
Here are some design drafts for the mobile app to control the lamp. The source file (Sketch) can be found under the link at the very top of the page.
Color Adjustment
Brightness & Sun Tracking
Implementation
As the target platfrom is only Android for the moment, i will implement the app as a native Java program using the official Android Studio IDE.
For the circular adjustment slider, i found a pre-made widget by devadvance.
The Bluetooth Chat Example gives me a starting point for the bluetooth interface to my lamp.