If the image comes as a .png, then I save it how it currently is. If it's in any format other than .png, save one certain time, then when I have finished editing it, I save it as a .PNG in MS paint.
*Looks at the current image, then looks at an earlier one* Holy cow. You're right. It's definitely getting darker. Sorry. I don't know how on earth that's happening. I'm not sure if I'm the only one causing this, but I'd probably better step away from this thread unless you're mistaken and it's someone else.