Colorblindness is caused by missing one or more of these cone cells. If you have none of the cones, it is called achromatopsia.
I'd be interested if there is any biological explanation for why our cones are oriented in this way. Like for example, there is a lot of overlap between the efficiency curves of rMr_MrM and rLr_LrL.
So different cells have different sensitivity to a color with certain wavelength. I wonder will people be more sensitive to a certain color than others?
One reason for why we have so few blue cones compared to red & green cones could be that it was more advantageous (from an evolutionary perspective) to distinguish between different shades of red & green for purposes of finding food, evading predators, etc. than it was to distinguish between those colors and blue.