Since I always have the wrong background color selected while moving sprites around with brush selection, it often goes like this.
I started using the ‘Set background as transparent’ function so that the transparent color is the currently selected background color.
It seems to work well with rectangular selection but if I do the same with a freehand selection, I still have a rectangular color shape around my selection.
Also, I just remembered something. Wasn’t there an option in old Pro Motion builds so that when you make a rectangular brush selection, the program would look at the color in the four corners, and if the color was the same in these corners, it would detected it as the background color of your selection ?