Seeing Differently
Approximately 300 million people worldwide experience color vision deficiency. For most, the world is not grey — it is a different palette. Protanopes and deuteranopes see blues and yellows clearly but cannot distinguish reds from greens. A ripe red strawberry against green leaves may appear uniformly brown. Traffic lights look the same except for position. This simulator transforms any color through the lens of each deficiency type, revealing the perceptual gap that affects 1 in 12 males.
The Biology of Color Vision
Human color vision depends on three types of cone cells in the retina, each sensitive to different wavelengths: long (L, red), medium (M, green), and short (S, blue). Color blindness occurs when one cone type is missing or altered. Protanopia (missing L cones) and deuteranopia (missing M cones) are X-linked recessive conditions, explaining why males are affected 16 times more often than females, who have two X chromosomes providing a backup.
Simulation Methodology
This simulator uses the Brettel-Viénot-Mollon algorithm, which projects colors onto the reduced color space of each deficiency type. Normal trichromatic vision maps to a 3D color space; dichromatic vision collapses this to a 2D plane. The transformation matrix for each deficiency type projects every color onto this plane, accurately approximating the perceived color. The severity slider interpolates between normal and full deficiency to model anomalous trichromacy (partial deficiency).
Designing for Everyone
Accessible design is not just ethical — it is practical. When 8% of your male audience cannot see red-green distinctions, relying on color alone to convey information (red for errors, green for success) excludes millions of users. Best practices include using shape and texture alongside color, adding text labels to color-coded elements, choosing colorblind-safe palettes (blue-orange works well), and testing with simulation tools like this one. The Web Content Accessibility Guidelines (WCAG) formalize these principles for digital products.