Actually I drew inspiration from Paintweb but found that it had not been updated since 2.5.
Since Atto is the way forward and we are standardising on 2.7 with Atto at my workplace I decided it was easier to just write a new plugin for Atto than to try to crossport Paintweb from TinyMCE to Atto.
I may look at reproducing the feature set from Paintweb.