Set Transparency now "works", bugs with fill

It was never actually changing the color before but now it should be
working properly. If I fill the entire drawing area with black for the
background layer and green for Layer 1, Layer 1 covers up the background
as expected because the objects begin as opaque. If I set the
transparency to 0% then we see black as expected. But if you click 50%
transparency for Layer 1 it displays an interesting pattern.

There have also been some interesting bugs with the fill now. If I draw
a circle and fill it with black in the background layer, and then make a
new layer, select all layers, set Layer 1 to the current layer, and then
fill outside of the circle with green... It displays properly at first
but then looking at just Layer 1 the entire drawing area is green except
one random white line, and if you display both the image is green with
our black circle covered up.