User blog comment:Bovell/Color blind assist option for Modern Warfare 3. Killstreak system reworked./@comment-402843-20110708161254/@comment-670668-20110708163059

Red-green color blindness causes them to have difficulty telling the two apart.

A well-known test image is a green circle with a red number in the middle. People with red-green color blindness will have trouble seeing the number, if they can at all.