How does a photon have different energies?

The energy of a photon is proportional to its frequency. In math talk E ~ f. And that means we must have a constant of proportionality to make the proportional into an equation. And that constant is Planck's Constant, h. This is a very very very tiny number; look it up.

So the energy of all photons is found from E = hf. Note that he speed of a photon, C, is nowhere in sight in this relationship.

Where the frequencies are the highest, the photons have the highest energies. At the extreme end these are called gamma rays. At the lowest end, where the frequencies are the slowest, we have radio waves like very low frequency (VLF) radio waves. Somewhere in between these two extremes lies the visible light spectrum, which we memorize as ROYGBIV for the colors red, orange, yellow, green, blue, indigo, and violet. On either side of R and V lie infra red (IR) and ultra violet (UV).

So, physically, the difference between a high and low energy photon is the frequency...and that's all.

So your real question is, can a single photon of a given frequency be interpreted as the color green? Probably not. Not because it would not register as a green color in your brain, but simply because one photon would be way too dim for you to see and interpret as green. You see, brightness is a function of how many photons impinge on your retina, at the back of your eye, over a period of time. And one photon, even though it's at a green frequency, is just not enough when it takes billions of photons just to be seen as light by the human eye.

OK, we'll try to get at this painlessly.

A photon moves along a line, point A to point B. That is the one that gives the speed of light.

At the same time it also wiggles up and down; this factor gives us it's frequency.

Wavelength, frequency, color, energy state: are all terms saying the same thing (the wiggle speed).

A high energy photon was produced in a more violent reaction, and tends toward the ultraviolet.

Green happens to be my favorite because it's almost mid-range in the color spectrum; and like resistor color codes gets the number five. 5 thousand angstroms wavelength.

It's like waves in an ocean. You've got small waves with very little energy, and you've got large waves with tonnes of energy. And they travel at the same speed.

The small waves are like the low frequencies in photons while the large waves are like the high frequencies.

The green question is yes. Red has a lower frequency and blue has a larger frequency.

As to what a photon's frequency, I mentioned waves, the up and down motion in the water. The frequency is how often it goes up and down. The "up and down" is actually how often it goes from being an electric field to a magnetic field, hence why it's known as electromagnetic spectrum.