try gimp, search gimp on google, it has the hotkey for chging forground to background colors by pushing x, im not sure if you can lock the transparency but ive never tried that, instead of soft paint brushes you can use the tool airbrush, which has the options of pressure and rate, not hard to make lines although tricky, you must use the path tool then stroke it... but still easy. sorry but you cant merge selected layers on gimp, but you can copy the layer then delete it, then merge them all then paste the layer. thats all i know, im sure ill get banned for dissin paint.net, it rocks but not enough tools for me, peace out have fun!