Looks to Ork Buggies and Trakks, raises eyebrow....
But still, Marine Bikes are long overdue an overhaul.
As for these rumours, I don't think it would be new box art. GW tend to stick to a single colour scheme across a given range, to prevent confusion for non-hobbyists.
Believe me, it helps when a relative of a nerd comes in saying 'he wants some little blue robots for his birthday'. All vanilla Marine boxes feature Ultramarines on their front, narrowing it down in this case - though it is of course much, much easier if the kid is one of your regulars like. (though 'he collects Orcs/Orcs/Orks' remains a perennial pain in the bum, and much emphasis on retaining the receipt and that swaps must involve a still sealed product)
But point still stands - having different Chapters across different boxes just creates confusion as to which army they are for.