It happens to quite a few people that their eye colors get lighter when they cry. There are two main explanations for this kind of phemonenon. First of all, the eyes may get red after crying, and the redness may neutralize the original color of your eyes. For example, the brown and red are a pair of complementary colors in proximity which can makes the brown eyes appear lighter. The other explination is that the pupillas of human eyes will get larger when they are crying, thus making the iris of the eyes which determines the eye colors becomes larger. But the amount of the pigments that the iris contains are limited. Therefore, the pigments have to be distributed much thinner and wider, thus making the color look lighter. It is quite normal, do not have to worry about it.
When you cry, the tears in your eyes are convex lenses somehow.
The function of a convex lens is focusing the parallel rays from somewhere far away into one single light at the lens' focal spot , which, in this case, is a spot in your fundus.
Crystalline lenses in your eyes are convex lenses as well , whose focal lengthes are adjustable. When tears are full of your eyes, the focal lengthes get longer so you can see something far more clearly.
Well, yes, it is kind of normal to have this kind of situation. And as we know that we are born with certain eye colors. And it can not change with time. But on the other hand, you need to know that there are also some factors which can just lead to change in eye color. For example, emotion can be the most common one. So according to some researches, sometimes our eyes look to be a different color when we're sad or we cry. This is because our eyes turn red when we cry. The red color introduced to the eye alters the shade of the iris. And then, your eyes may look lighter than before.