No, at this time, no documentation really exists. I have been meaning to post some "pinned" posts here on Discourse about common issues with iRhino 3D. Usually, instead of doing that, I start trying to engineer away the bugs.
I'm not sure I fully understand what you want to do, but it sounds like assigning colors to objects.
iRhino 3D uses the material color assigned in Rhino...not to be confused with object and layer colors. In Rhino, select the object you want to assign color to and - in the Properties panel - make sure you have assigned a material to the object (we only support default Rhino materials, so far). Go to the Material settings (the tube of paint icon in Rhino 5 for Windows) and assign a color under the Basic Settings section. You can also assign a gloss or transparency setting.
iRhino 3D displays what the model looks like in Rendered mode (in Rhino 5 for Windows and Rhino 5 for Mac); not in Shaded mode. Once you have applied the colors, make sure you view the model in Rendered mode.
If assigning colors to objects is not what you would like to do, please help me understand.