Negative Capability

I find it interesting, maybe even a bit sad, that Keats thought that Newton ruined the poetry of a rainbow by reducing it to a prism. I wonder if this statement could be better understood when considered alongside his theory of Negative Capability, which he describes in his letters as "when a man is capable of being in uncertainties, mysteries, doubts, without any irritable reaching after fact and reason." It seems to me that Keats would find Newton guilty of "irritable reaching after fact" and destroying a beautiful mystery.