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    $\begingroup$ In theory yes a photon can be in a superposition of many different frequencies (frequency is basically equivalent to energy $E=hf$). But on measuring it, in any way, you will always collapse the wave function into a state of well defined frequency. $\endgroup$
    – Quantum spaghettification
    Commented Nov 9, 2016 at 21:50
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    $\begingroup$ Superposition of different frequencies as a state of a photon has little in common with mixture of photons (or waves) with different frequencies that produces white color. All terms of the superposition are monochromatic, they do not "mix", and each is a complete picture of what might happen observationally. So photon may exist in a superimposed state, but it won't be white. For the same reason superposition of dead and alive Schrödinger cats is not a dead-and-alive cat, despite the popular misconceptions, it is more like two cats in ephemeral "parallel worlds". $\endgroup$
    – Conifold
    Commented Nov 9, 2016 at 23:06
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    $\begingroup$ @Quantumspaghettification frequency is frequency, how can a photon have many of them? $\endgroup$
    – Bill Alsept
    Commented Nov 10, 2016 at 4:58
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    $\begingroup$ @BillAlsept The same reason an electron can have a (superposition of) an up spin and a down spin. A photon can be in two (or more) different energy eigenstates at the same time. On measurement you will only see one frequency, like on measuring the spin of an electron you will only see up spin or down spin. $\endgroup$
    – Quantum spaghettification
    Commented Nov 10, 2016 at 13:46
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    $\begingroup$ @SPARK There is a saying, (the origin of which I cannot find) that an electron is not a wave, nor is it a particle; it is an electron. The same holds for photons. I don't think considering it as a 'quantum energy packet' would help, this seems to imply that a photon has a well defined energy (/frequency) - it may not. I think the picture of a 'quantum packet of vibration' is more helpful if you want to go down that route. I visualize in the same way I visualize an electron - i.e. as a particle (like thing). $\endgroup$
    – Quantum spaghettification
    Commented Nov 10, 2016 at 13:55