User blog comment:DancePowderer/681 Abridged/@comment-94.254.85.112-20120911150639/@comment-4899461-20120911155729

I thought they were pants too, until Sff explained it better. The white space is actually Sanji's bones. Only the white space cracks, and the black space is just his legs. The grey outline of the leg is his pants. And look at the non-cracking leg, and you'll see Vergo's shoe is visible, and all of this fits the shot in the previous panel.

Plus, Vergo's pants are white, and they don't have stripes either.