That is the task of your eyes. Your brain is simply reading the codes sent from your eyes to present to you as “comprehension”. Your brain doesn’t see anything, ever. Your eyes see, and your brain takes the information presented by your eyes, and categorizes the information so that you have reference to consult in an ongoing basis. If your brain did not do that for you, every single thing would be new to you, every single time you encounter them. You would never know what is dangerous, or delicious, or cold.
Your eyes see light, and color, and sends signals to your brain for indexing. Many many things are cross indexed, so we know the difference between ketchup, and a red ball, or a car.
Sometimes memories are nothing more than your brain trying to sort out whether this item goes with that outcome, or not.
Dreaming is brain’s best chance to mess around with colors, textures, tastes, and such, and work through outcome potential, so the files stay fresh, and accurate. There only seems to be light, because brain happens to have some vision files open and active at the moment. It is nothing more that codes, much like the Matrix movies approach the subject of perception. If a someone else’s file system from their brain entered your brain’s files, you would suddenly be perceiving same old stuff in confusing new ways. See Jumanji, the remake, or any Freaky Friday movie.
In each case, the perception of others compared laterally with our own is at play in the story.
Light and color in dreams or memories have no more to do with actual illumination than dreaming about a delicious meal would fill your empty stomach.
K?