Is the use of colors in commercial marketing, such as painting a restaurant orange to stimulate appetite, considered among the permissible means, or does it fall under divination?

There is no harm in utilizing colors in commercial marketing, such as choosing colors that are appealing to people or soothing to their nerves. If it is proven through experience that people tend to prefer a certain color and it is used in marketing, then this has no relation to divination (kahana). This is because divination is the claim of knowing the unseen and foretelling the future.