add frequencies
Discussions of colors can sometimes become confusing because of the difference between light emitters and light absorbers. Light absorbers, such as dyes and pigments, absorb frequencies from those that you see, while light emitters add frequencies to what you see. If I were to shine red light, green light, and blue light into your eye all at the same time, you would likely see some variation of white. If I were to mix red paint, green paint, and blue paint together, you would likely see black or some very dark color.