From what I've studied about EM waves reflection over dielectrics, the reflected wave must have the same frequency than the incoming EM wave before reflection, else Maxwell equations aren't satisfied. So far so good.
However in practice I've noticed that for instance blue LED reflect as violet on white walls, pine needles, plastic and wooden floor to name a few.
I've also noticed the same similar shift from blue to violet while walking in the streets of a city in a thick haze night. When I far far away (farther than about 20 m) the lights appeared violet, while when I walked toward the lights, they were turning blue as I was advancing.
I couldn't find any explanation of how such a phenomenon could occur. I've thought about my eyes being tricked but I don't think this is the culprit. I had also thought about the material from which the light was being reflected off as absorbing better some frequencies than others, but since this occurs over almost any dielectric material I've seen so far, I also discarded this hypothesis.
I'd appreciate if someone could come up with an idea and also tell me whether he/she noticed a similar behavior.
Edit: I have just found the answer to this question by accident. My 2 years old son turned on a light bulb near a blue Christmas light. It turns out that when the two lights are on, the blue one appears almost violet, its reflection on the white wall is also almost violet. But when the light bulb is turned off and only the blue light remains, everything looks blue, no violet whatsoever!
So I conclude that it is really just perception. Incredible!!!