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If one had an electron gun capable of firing electrons with a specific energy at an object, can it change its colour?

I think it is possible because the emission spectrum of the material would allow it to emit photons of specific energy, which our photo receptors in our eyes perceive as colour.

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could you go into a bit more detail about what you are asking? – Jim Feb 5 '14 at 1:39
@Jim The title says exactly what I am asking. – Ruben Feb 5 '14 at 2:08
Understanding why you believe firing electrons would change the color may help tailor a response & explanation for you. – BMS Feb 5 '14 at 2:15
@BMS As I outline in the second paragraph, I believe it will change the colour because the fired electrons will excite electrons in the object's atoms/molecules/de-localised electrons. After they return to their normal energy state they emit a photon. This photon I believe should be observed as colour. – Ruben Feb 5 '14 at 4:46

Yes, it is possible, it is called Cathodochromism. It can only be induced in certain Photochromic materials and the coloring might be reversed by applying another process, which involves removing the electrons.

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So this is a permanent colouring? Because what I expected would be a temporary colour change for the duration that the electrons are fired for. And why do only Photochromic materials have this effect? – Ruben Feb 5 '14 at 11:35
It is temporary and usually can be "bleached" with light. If the photochromic material cannot be completely erased, then heat will do the trick. They have this effect because you cause temporary reactions at the atomic level that will show to us as a dramatic change in colours. These materials have been used extensively in dark trace tubes mainly for Radar. – CAGT Feb 5 '14 at 13:53

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