Reed settled on a reindeer. 'Reindeer in Here' book and plush gift set is born. Reed found an illustrator, Izzy Bean, who worked up about 50 reindeer to pitch to a focus group.

Why reindeer eyes turn blue in the dark Arctic winter. Here's looking at you: A close-up view of a reindeer in the Arctic. Kia Hansen. Oct. 30, 2013, 12:44 PM EDT. By Charles Q. Choi.

A reindeer with a blue tapetum sees less clearly than one with a gold tapetum, but its eyes are 1,000 times more sensitive to light. “Clinically, the reindeer become glaucomic,” Jeffery said.

The eyes of an Arctic reindeer also do this, but because of the seasonal physical changes to the tapetum lucidum, the wintry blue eyes reflect 50 percent less light than the golden eyes of summer.

A reindeer with a blue tapetum sees less clearly than one with a gold tapetum, but its eyes are 1,000 times more sensitive to light. “Clinically, the reindeer become glaucomic,” Jeffery said.

What color are reindeer eyes? Depends on the season. An astrophysicist and an eye expert teamed up to solve the mystery of how and why reindeers’ eyes switch from yellow to blue in wintertime.

Reindeer eyes change color during the winter, from golden to blue, something researchers say helps them to capture more light during the Arctic's dark winter months.