It does however make you wonder why a company that can afford such a large advertising budget would use secondary spelling variations rather than the preferred Australian English spelling. On the company's About page they've used the spelling colour, ("we do not promote do-it-yourself home hair colouring") which does indicate inconsistency.
My concern with advertising signage which doesn't use the preferred spelling is it can cause confusion when people regularly see alternate spelling variations. Buses are regularly used by students and I'd be fairly certain most teachers would mark the spelling "color" as incorrect.
The preferred Australian English spelling.