The first milk that comes out from the breast (also called the foremilk) is thin and watery, The milk that comes out later is thick and white (hind milk). The former contains lots of vitamins and water required for the baby while the latter is rich in fat. Together, they meet all the nutritional requirements of a baby up to 6 months of age. So, your observation is absolutely normal. Make sure your baby empties one breast completely before being offered the other breast to get benefits of both foremilk and hind milk.