When the user selects an area on the canvas I know the convention is to identify that by shading the selected area with that blue color (until another tool is selected). Might I suggest changing that so that the selected area is the part that retains it's visual appearance and that the unselected part of the image is the part that changes.
I often click on the canvas with the selection tool to unselect what I am working on, after which I switch to say the paint brush tool only to find nothing is being drawn to the canvas. Needless to say I have accidentally selected a few pixels without noticing. If the unslected part of the image was darkened for example that would become immediately apparent. It would also make the selection clearer which makes more sense to me.
Heres a visual of what I had in mind.