@Drydareelin: I am not able to find a way to do this either. RIght clicking or changing the first and second color does nothing
I have some feedback regarding the way you draw your toolbar items: You draw every dropdown button as if it was a splitbutton. This is confusing. One only opens a dropdown menu while the other also cycles through its items depending on where exactly you click it. But the way you draw both buttons doesn't indicate this difference at all. There should be no seperator on the normal dropdown button, only on the splitbutton:
And then I have a personal problem that I think not many have: On my laptop, which probably has a bad IPS display, it's super easy to lose the selection cursor (cross) out of sight. When I move it at a certain speed over the grey background surrounding the image or over the checkerboard background, it seems to disappear completely and makes for some funny but annoying moments. Because I have no mouse connected to my laptop but only the touchpad it's important to see visually where the cursor is, you don't feel it in your hand like when you're holding a mouse
I realize that you won't change the cursor because one guy has a bad lenovo ips display, but can you load the cursors at startup from the paint.net directory? That would help a lot if I could edit the .cur files to find a way that works better for me.