Hey! 
I’m used to planning out my structures in case those are too monstrously huge, so I’ve ran into this issue… In the old builder, one could use the path tool to recolor the blocks by drawing big rectangles. Now, path on path creates another level, so one has to resign to using the brush tool, which only colors one bit at a time, forcing you to spend a lot of time coloring in the shapes.
So, I would suggest to have a key, let’s say SHIFT, to switch the tool from coloring one block at a time, to lock and fill in on release.
Could this either become a part of 1.1 or is there a modder who could look into this? 