11. Nine percent of men and one-half percent of women are color-blind

  Color blindness doesn't mean blind to all colors, it refers to a deficiency in the cones of your eyes causing them to have trouble seeing a difference between colors.  Color blindness can come in many forms, the most common is difficult distinguishing between reds, yellows and greens.  When designing and you use color for meaning such as having any text in Red mean it needs immediate attention, consider adding an extra layer of redundant coding to the importance like any text in Red with a box around means it needs immediate attention.  This extra layer can help those with color blindness decipher the code without need to see specific colors.  Consider colors that work for everyone, a color scheme with varying shades of brown or yellow. Avoid red, green and blue.  Test out your images and websites with colorblind tests online.