We can actually use this to our advantage. If you don't like chick lits (sorry, but it is just such a great example), stay away from pink and purple. Easy as that. The colour of a cover often says more about the book than those magazine blurbs, e.g. ABC newspaper says "Fantastic book!" or XYZ critic "Best novel since ..." I don't even have an idea about the content there.
Both the colour and the jacket design tell us a lot about the book, about the reader it is looking for. We can guess the genre, the style, even the story. That doesn't mean it isn't misleading sometimes, but generally, it is a good help. Recommendations from friends or other helpful readers, articles about a book, reviews on your favourite internet pages, they all contribute to getting a good selection of literature appropriate for the individual but if you're on your own when you come across something new, which is your favourite colour?
So, go ahead, judge books by their covers! Pick the ones that appeal to you most. The most important part is, that you read those you might like most. After all, you are reading the novel, not the cover.