Yeah, it is true. This is said to be in relation with body temperature. Do you know that your body temperature will be different when you have different moods? In other words, when you get angry or worried, your body temperature may get higher. On the contrary, your body temperature will be normal when you just feel calm. I can not guarantee everyone has this situation, however, as for me, I have. When I am high, my blood will get hotter and then my eyes will change from blue to light green. But when I feel calm again, my blood just returns to its normal level and then my eye color just goes back to blue again.