QuoteOriginally posted by: outrunQuoteOriginally posted by: FermionQuoteOriginally posted by: rmaxQuoteOriginally posted by: outrunit's always red but de Brolgie matter waves are different from photon wavesIndeed and colour is from photons reacting with your retina. If electrons reacted with the retina you have have something analogous to a CRT.This distinction between electron color and photon color is off-track. Do we say that the sky has no color? No, we say it is blue during the day, because that is the predominate color of light coming from the sky when the sun is high and we talk about the red sky in the morning or evening.Likewise, the color of an electron is given by the frequencies of the photons it emits or resonates with. Sodium electrons, for instance, are predominately yellow when excited -- which is why burning sodium shows a yellow light.Hmm.. this is very fuzzy. Electrons don't have a color without context. You mention "Sodium electrons" but that's not a type of electron, those electrons are indistinguishable from Silicon electrons which gives a very different emission pattern when excited. The photon absorption / emission of atoms is also a completely different things from matter waves of electron itself. The Rayleigh scattering of blue light in the sky is *yet* again something different. It's an atmospheric filter function of the photons emitted from the sun (and the reaction between the photon and the retina).Color originates in the retina where a signal gets fired to the brain due to some stimulus. Some stimuli -like firing an electron beam in someones eye- probably won't give a color sensation.Indeed! The emission lines of sodium are as much a function of the sodium atom's protons as they are a function of its electrons. Moreover, once a sodium electron has emitted it's yellow photon, the electron is no longer yellow.The retina transduces wavelength-related information on populations of photons over a region of the retina (the eye cannot detect the colour of a single photon). The brain interprets and assigns the detected patch of colour to a corresponding object in the visual field (note that there's all sorts of artifacts and approximations in this system -- in essence, the brain paints sloppy patches of color onto a black-and-white line drawing of the scene). Whether a given type of object has color then depends on it consistently and persistently reflecting or emitting populations of photons of a limited range of wavelengths. Electrons, in general, don't do this.Of course, we can extend the notion of colour to single photons (which is something the eye can't do) and we can further extend the notion of colour to be a range of wavelengths or energies.