In my experience with cold casting, the darker areas can be caused by excessive sanding or insufficient aluminum content in the mixture, and is more prevalent on vertical surfaces when casting. However, you're not going to get the accustomed shiny finish that's produced with Rub n' Buff because it's a wax. The cold cast will be more dull and should have the screen accurate abraised metal look to it.
Regardless, I don't want you to be stuck with a helmet your not happy with. Feel free to return the helmet for a full refund. I can also offer to cast you another helmet with a higher aluminum content if you want to see if you get better results. Either way, just let me know.
