It's called *gasp* a PLOTHOLE! How many episodes are there of Dragonball Z? 276 episodes (excluding the original Dragonball, the movies, and Dragonball GT). Don't you think that somewhere in those 276 episodes they would forget a few things? Or that they needed to change a few things to progress the story, but couldn't think up of an excuse? They forget to explain things, leaving a hole in the plot. Hense, a plothole. Though the size of the plothole depends on how big the mistake is. King Vegeta's hair color not being black is a small plothole.
Remember, Vegeta's hair color wasn't originally black either. When he was on his way to Earth, his armor was a totally different color as well. He had greenish armor and brown hair like his father did. But he had the regular blue, white, and brown armor when he arrived on Earth. Then, later on, during the Namek saga (or afterwards) Vegeta actually grew taller and had black hair.
They changed the appearance of Vegeta as they changed and evolved the character. Though they never explained what happened to Gohan, Vegeta, Trunks, or Goten's tails. All saiyans are born with tails, as we know from the first season of DBZ. But after the saiyan saga, Gohan's tail never grew back, neither did Vegeta's tail. Neither mirai or chibi Trunks were shown with tails, along with Goten. Pan certainly wasn't shown with a tail, and neither did Bra (Bulla in the states, ugh). WHAT'S THE DEAL WITH THE TAILS?!?!? Now THAT'S a plot hole!
Back on topic, it's good that someone made something else besides another red suit teen mystic gohan, USSJ Vegeta or a battle damaged Goku. We need new original models for ESF, instead of the same recycled characters.
best be hurrying now shall we?