glv
5
This topic inspired me to update my “simple” draw program:
Mostly just having fun with this and keeping it very simple. 
The scrollbars in the Processing examples are worth taking a look at.
I modified the Processing example program and did this (early version) and was able to put this on my Android devices also:
I have a version somewhere that changes color as well and saves favourites.
You may also get some ideas (searched for RGB) from:
This is a Bluetooth RGB app I can use to control (serial over Bluetooth) my Arduino (an RGB LED) and Processing window (circle changing colors):
