Well, I'm no scientist, but my understanding is that the best scientific theory of colour still posits the interaction between the eye-brain, light, and the surface of outer objects that reflect light into the eye. So plants appear green because chlorophyll reflects green light which the human brain indeed processes in its human way. Alien eyes might see green differently.
In any case, it's once again too strong, I think, to say that colour is a "hallucination" or a delusion. There's an outer, physical system involved in producing the colours we see. Indeed, by talking about how the brain alone produces colour, you're assuming a distinction between the reality of the brain and the delusion of our perceptions. But we know about the brain via those same perceptions. So there's a contradiction in that analysis.
From the Wikipedia page on "colour": "Physically, objects can be said to have the color of the light leaving their surfaces, which normally depends on the spectrum of the incident illumination and the reflectance properties of the surface, as well as potentially on the angles of illumination and viewing."
