Tamed dogs that have dyed collars will lose the initial color of their collar, and will change to to opposite dye that is listed in the materials section. This bug is prevalent when updating from 1.7.10 to 1.8 pre. Until now the general consensus was that the dogs just had the wrong color collar. However upon closer inspection, it appears that the color that they were dyed was reversed in the order that they are listed.

I'll attach a video to better explain this bug bellow. It's under 3.5 min long, and worth a watch. http://youtu.be/I0-Ca_WwL_M