The physics and biochemistry is not on the side of these buses actually being red.
I would like you to elaborate on this concept. Because if the surface of a red bus did not have a physical structure which, either due to reflection or refraction, cause a preponderance of light with a wavelength between 620nm and 750nm to be redirected toward our eyes, it would not appear to us to be red. Similarly, plants appear green to us because they really are green. The pigmentation of the plant reflects primarily light between 520nm and 560nm because that is the wavelength of light which is least useful to the plant. The color of the plant conveys useful information about the biochemical processes of the plant. And if the plant is bearing red fruit, that coloration is usually conveying useful information, as well, about the ripeness of that fruit. Red fruit evolved prior to the advent of humans, and so it is safe to say that the coevolution between plants and animals such that plants are able to communicate the ripeness of their fruit to the animals they are attempting to bribe with that fruit occurred independently of the concept of red.
Colors are in the world, as wavelengths of light, independently of a conceiving mind. Minds far less complicated than ours- animals which really cannot be said to have minds at all- rely upon the perception of colors for their survival. Given that these animals lack the neural architecture to invent colors, it seems reasonable to conclude that there are real stimuli out in the world which correspond to colors.
Red being an angry color is in your head. Red, itself, is in the world, as wavelengths/frequencies of light.