Pro cure is http://www.pro-cure.com/ 6 drops in 6 oz is a good start.
burnt, scorched plastic will be as mundane as discoloration. Darker colors might not really show this.
with fresh plastic, I would try it again. Heat the plastic for 2 min, stir, heat for 2 min, stir, repeat this until it is cooked all the way through. plastic will be clear.
then add your color.
I have had greens/black not change color. But florescent yellow has turned orange due to over heating the plastic. heat stabilizer has helped solve this problem. Keeps bright colors bright.
As far as worm oil, its a packing tool. I dip the heads of the lures in it, then open the bag and insert the lures into it. The oil keeps it from sticking to the bags.
it adds nothing to the worm but it does feel neat in the bag. You can add scent and get the same affect.
Dont get me wrong, I use it and mix it it with scent, and even use it to thin the colors with when needed.