Well, I have conducted a few tests on this pirates legs and the problem seems to be a mold problem.
The blue is one colour plastic and the brown is also plastic, no paint at all.
I took a craft knife to the legs and scraped several areas of both colours, if it was paint then I would have quickly removed it. Even what looks like over spray on that triangular part on the left leg is solid brown plastic, I know this because I cut a piece out.
So my theory is that the right leg moulded Ok but for some reason the left leg didn't get enough blue plastic in the first place. The brown plastic then filled up what should have been blue and If you look again at that leg you will see the plastic is speckled, maybe air bubbles in it. As for why they didn't go ahead and paint the stockings on this leg is still a bit of a mystery.
