— Sorry Just updated more information on the post to avoid double post, it is legacy it isn't part of the master template and isn't being updated. Has nothing to do with anything with construct 2, sorry for the confusion.
As for undo functionality, it isn't a good idea to save the image rather have the brush marks as their own objects, so you can destroy them or make them transparent entirely in order of last created.
Doing this would allow you to tint the brush objects, and mess with their transparency(something I didn't do in the template), along with that you can make different shapes by having them as sprite objects, the only down fall is performance might not be good depending on how far you want the undo functionality to go back.