National Different Colored Eyes Day on July 12 is all about heterochromia iridum. It’s okay, we didn’t know what it meant at first, either. Heterochromia iridum is a term for the variation in color that gives a single organism two different colored eyes. It has been known to occur in populations of many species since the dawn of recorded history and is an interesting and sought-after trait. Only the lucky 1% of the population enjoys this special pigmentation, though there are three distinct types of heterochromia. Today, many people prefer pets with this fun eye color difference, and colored contact lenses are used just to mimic the trait! All this to say, give your friends with heterochromia a little extra love today.

There are actually three different kinds of heterochromia iridum – complete, segmental, and central. Central, the most common, appears as matching irises with different colors encircling the pupils. Many don’t know this classifies as heterochromia iridum! Segmental heterochromia appears as a different patch of color in only one iris, and complete heterochromia is the most iconic – two irises of different colors.