SetContext?

Well Im back to this, blending with alpha but when using the undo button the shapes shade gets darker, the alpha stays the same though. I’ve got a video for explanation here:
http://www.youtube.com/watch?v=bBvcZvNtnEU

After the undo if I draw another ellipse it seems to go back, but it doesn’t quite get there… This is what the undo function contains:

        screen = lastimg:copy()

The lastimg is an image which is drawn to at the start of every touch which saves the current screen.

And the function for saving lastimg is:

        setContext(lastimg)
            pushStyle()
            background(0,0,0,0)
            sprite(screen,WIDTH/2,HEIGHT/2,WIDTH,HEIGHT)
            popStyle()
        setContext()

Any help appreciated, thanks!

ResetStyle() after pushStyle()?

The push- and popStyle aren’t needed, I believe, because you aren’t changing any styles, but Jmv38 may be right in checking that you haven’t accidentally left any styles changed from previous drawing, with Resetstyle()

The culprit may be the black background. Why set it black when the drawing screen is white? That is an obvious reason why the transparent parts of the drawing are getting darker.

Same happens with white, black (as advised previously by another user) is used to stop addition of colour values. I had a problem like this before except it was different-ish

Put this in my undo function instead of copying the image and it works :s
Maybe the problem was just copying the image without drawing after?

--screen = lastimg:copy()
            setContext(screen)
                background(0,0,0,0)
                sprite(lastimg,WIDTH/2,HEIGHT/2,WIDTH,HEIGHT)
            setContext()