Traffic signal color recognition is a problem for both protan and deutan color-vision deficients.

Human Factors, September, 2003 by David A. Atchison

INTRODUCTION

Approximately 8% of males and 0.5% of females in the population have congenital red-green color-deficient vision. There is little true color blindness (~0.0005%; Pokorny, Smith, Verriest, & Pinckers, 1979). These people have reduced ability to discriminate redness-greenness throughout the full gamut of colors. Most significantly, from a safety point of view, the problem includes the red, orange, yellow, and yellow-green parts of the visible spectrum.

Red-green color-vision deficiencies are subdivided into a number of categories (after von Kries, 1899):

People with dichromasy lack one of the three normal receptors. As a ...