Reindeers’ Eyes Change Color With Seasons
The arctic reindeer is the only mammal whose eyes shine a different color depending on the season. In summer, when the sun is bright, the eyes are dazzling golden, but as the sun prepares to set for the winter, the eyes become less reflective until it turns dark blue in the dark winter months.
https://www.amusingplanet.com/2019/10/reindeers-eyes-change-color-with-seasons.html