If you haven't already know, Jubut Rud Cloack has been shrouded in veil of mystery. Jubut-rud means "Mighty Cloak" in pseudo-Khuzdul and it has special ability. As you can see on the screenshots this cloak can be dyed.
This is just a quirk of the appearance system. Some cloaks are set up one way, some cloaks another, and the dye preview window doesn't handle one of those cases correctly.