User blog comment:Dettles/Questions about haki/@comment-8823907-20130620114043/@comment-8823907-20130621125418

Well AWC. You could be right. But to be fair the kuja wariors were using haki imbued arrows. Boa Marigol and Sandersonia were striking luffy using haki. Rayliegh was using Haki against Kizaru. Marko kicked kizaru with haki, also he Kicked Kuzan. Jozu attacked Kuzan with haki. Even WB attacked Kuzan with haki (one of the soldiers mantioned that he was hit by a haki imbued hit). WB was destroying akainu with haki. Maco and vista attacked akainu with haki. So you see there have been attacks with haki and none of the above mentioned had the blackened limbs.

There is only one scene which makes me think that maybe there is a distinction between normal haki imbued punch and the blackened imbued punch and that is the sene vere pecoms hits caribou. If that was simply an animation mistake than i believe that the reason why they have black limbs now is that Oda didnt think of it at the time.