The first concept to keep straight in your mind is the difference between reflected light and emitted light. We observe our surroundings through the reflection of visible light, emitted by our Sun or man-made sources. Emitted light is composed of photons generated by the matter emitting the light - it's an intrinsic source of light. Reflected light consists of photons whose origin is elsewhere but reflected from some object. Let's now confine our discussion to just the regime of visible light, with wavelengths between 400 nm and 700 nm.
Color is our brain's interpretation of our eyes' detection of different wavelength visible light.
Each type of cone is sensitive to a broad range of visible light, but this sensitivity is bell-shaped, peaking at a particular wavelength, with lower sensitivity for wavelengths away from the peak. Our perception of color comes from the brain's interpretation of how many photons of particular wavelengths fall within each of the 3 types of cones. For example, an equal mixture of red and green light is interpreted as yellow , equal mixture of red and blue light is interpreted as magenta , and equal mixture of blue and green light is interpreted as cyan . For example, pink is the combination of yellow and magenta light, or equivalently due to the combination of red and white light. Because the cones' sensitivities overlap in wavelength, any colored source of light will appear white if it is intense enough.