We have chemicals in our eyes that are able to see light of certain energy levels. When one of these chemicals sees light of that level, the cells containing that chemical tells the rest of our brains that we've seen that light. Our brains then tell us that we've seen the color of light that has that energy level. It all happens because of the way that our brains are wired - light has color because of what our brains see, not because of the energy of light itself. We have chemicals to see the colors of light that we do because those are the energy levels that the sun emits the most of. Had we evolved on a planet orbiting another star, we would see colors of light that match the light coming out of that other star.

It is probably easiest in this case to think of light like a wave. Different colors of light correspond to waves with different frequencies. This is to say that different colors of light are just waves that oscillate (that is, swing back and forth) a certain number of times per second. For orange light, the wave oscillates 500 000 000 000 000 times per second. Blue light waves oscillate more quickly (higher energy), and red light waves oscillate more slowly (lower energy).

To think of why higher frequency waves (or waves that oscillate more quickly) have higher energy, imagine you have a rope and you're trying to swing it back and forth. It's easier to swing the rope back and forth slowly, and the faster you want to swing it, the more energy it takes.

Light travels as a wave packet, and packets of light always travels at the same speed in one given material. For example, red light packets and blue light packets have the same speed in air.

The difference in energy between red and blue light has to do with wavelength inside of the packet. Wavelength is the distance between two peaks of a wave (see below). Red light has longer wavelength, and blue light has shorter wavelength. In other words, blue light has more energy, so it oscillates more within the packet than red light does.

wavelength