It's only a dumb question because I don't see it being true at all. There are hundreds of big casinos out there and I have seen every variety of color scheme, but one thing that they do want to be is recognizable and this is definitely easier when you have a highly contrasting color scheme. It helps when it comes to advertising as well, because these places spend many millions a year all over the world and in some highly prominent places, but one side benefit is the unconscious pull that seeing certain color combinations will have on a gambler. It can trigger them to visit again if they make that association in the back of their mind. There's nothing special about a black and green combination, but there are only a certain amount of combinations that look good - so there will be plenty of overlap between brands.