This part of Chromaticity estimates whether colors are easily discriminable by using empirical models that predict "just noticeable differences" (JND). In Chromaticity, JNDs refer to whether you can reliably tell two colors apart from one another.

The first slider – Percent (Conservativeness) – allows users to define how strict they want "reliably" mean in for color discriminability. A 50% would mean that 50% of people could easily differentiate the two colors. While empirical studies often set JNDs at 50%, stricter thresholds may make more sense in practice.

The second slider – Size (Visual Angle, degrees) – refers to how large the pixels are on the screen and ultimately on your retina.

Color vision deficiency (“color blindness”) refers to different mutations that affect color perception, and affect roughly 8% of men and 0.5% of women.

While red-green color deficiency is most common (deuteranopia), several other types exist and are caused by missing different types of cone cells. There are also less severe color vision deficiencies where most but not all colors can be seen, which is caused by weak rather than missing cone cells (e.g., deuteranopia vs. deuteranomaly).

If you'd like to know more, http://www.color-blindness.com/ is a great source of information.