Instead of using on-screen sliders and buttons to tweak colors and other properties I decided to try MIDI. Simple MIDI devices are cheap and have enough features so I got myself a Korg NanoKontrol and a Korg NanoPad.
The application running on a Windows PC communicates with the USB MIDI devices and passes the information to the Android (HTC Desire Z) and Maemo (Nokia N900) devices over a TCP socket (WLAN). The application features a spinning logo with tweakable material values and postprocessing properties. The graphics are drawn with OpenGL ES 2.0 and the MIDI data is used to modify the shader uniforms and camera position.
The next step is to record the data. It can then be used in demo projects by playing it back.