I have a game project where you create a custom car and then
you can have the image emailed to your email address. The image
that is being exported has green artifacts in it.
The project is a multiple choice quiz with 6 questions. If
you get a question right, you get to choose a car body (BMW, VW,
Muscle Car). Second question gives you color choice. Third question
gives you decal choice, etc.
So all of the artwork is located in separate layers and the
script reveals the correct layer based on the choice made.
The artwork in the game is comprised of PNG files with alpha
to be able to composite on the fly.
The artifacts that appear are green and red and appear within
the image and not on the edges, so I don't think it has anything to
do with the alpha channels of the PNG.