Understanding the three main deficiency types
Color vision deficiency comes in three primary forms. Deuteranopia (missing M cones) and protanopia (missing L cones) both cause red-green confusion — reds and greens appear as variants of the same brownish-olive tone. Tritanopia (missing S cones) causes blue-yellow confusion — blue and purple can look similar, and yellow can appear pale. Each type affects a different portion of the spectrum, which means a palette that is legible under deuteranopia is not necessarily legible under tritanopia. Designing for all three requires building luminance contrast into every color distinction that matters — because luminance is the one dimension that all deficiency types preserve fully. Testing with a color blindness simulator (rather than guessing) is the only reliable way to verify a palette against all types.
