Originally Posted by HarryT
With the very greatest respect, I've answered this question at least half a dozen times already. It's because the colour fringing is due to very slight non-parallelism in the two faces of the light diffuser. These are difference of the order of the wavelength of light - ie way, way below what any reasonable manufacturing tolerance can achieve.
Yes, I know I read a post of yours where you mentioned the light diffuser being the cause, but I didn't recall reading the exact reason behind it. I see what you mean now, that makes sense.