Generally speaking, there is not an effective way to know the eye color of the baby when the mother is still pregnant. The eye color of people is usually determined by the amount of pigments contained in the iris of the eyes, which is decided by the heredity and gene selection of each individual. And sometimes the environment that a pregnant woman stays in can also have some influence on the gene selection. Sometimes, the eye color of the baby is tha same as that of its mother, sometimes its father, and even sometimes ite eye color is different from both of its parents.
Well, in my view, I think babies' eye colors are usually decided by their parents' eye color. But in most cases, brown and green are considered as common eye colors. It means that if your parents are neither of these eye colors, but you still get a chance to get these two eye colors.