Often I find that I want to change the color from one object to another and stencil or paint bucket are just too slow.
Try this trick, In mode select formula then go to tools and settings add this will open up the dialog for programming the brush. Now enter in in the “left mouse buttton"if(a==bg,fg,a)** and enter in in the” right mouse button"if(b==fg,bg,b).
Now when you select the foreground color as the one you want to change to and the background color you want to change from it will work and it will not effect anything that is’nt the background color.