What type of color deficiency results in an inability to distinguish between red and green?

The inability to distinguish between red and green is characteristic of certain types of color deficiencies known as red-green color blindness. Protanopia specifically refers to a condition where individuals cannot distinguish red light due to the absence of red cones (cones sensitive to long wavelengths). This leads to confusion between reds and greens, as well as a dulling of reds and pinks.

It's important to distinguish Protanopia from other types of color deficiencies. For instance, Deuteranopia also leads to challenges with red and green distinctions but is tied to a failure of the green cones. Tritanopia affects differentiation between blue and yellow colors, not red and green. Achromatopsia, on the other hand, represents a complete absence of color vision, meaning individuals cannot perceive any colors at all, which is a different and more severe condition. Thus, Protanopia is the correct answer as it specifically identifies the inability to tell apart reds and greens.