The professor mentioned color filtering the separate RGB channels. A Russian photographer Sergey Prokudin-Gorsky took many color photos in the early 1910s before color photography was common. He did so by taking three black and white photos for every photo, each taken through a red, green, and blue filter. These photos can then be combined to create a color photograph (physically through filters or digitally by putting each pixel value through the correct color channel). The process and collection of photos can be explored here: https://www.loc.gov/exhibits/empire/making.html
On modern photosensor arrays, there are actually twice the number of green-filtered sensors than blue and red ones (as visible in the first picture). This is known as a Bayer filter https://en.wikipedia.org/wiki/Bayer_filter. The main reason for this is to better mimic the human eye's sensitivity to the color green.