Hi,
Yes you can, just look on the CustomObject have a constructor with a customColor (float[]) parameter.
try this on the CustomActivity
someObject = new CustomObject("test", "patt.hiro", 80.0, new double[]{0,0}, new float[] {1.0f, 0f, 0f, 1.0f});
last parameter I asume is RGBA values, this will show red cube on hiro mark
Regards
Mariano