A.S.
The colostrum is what you have right after baby is born, it's yellowish-clear.
When you pump you will notice that your breast milk looks different when you pump it in the beginning and end. In the beginning, you pump fore-milk. This milk is more watery and usually more clear. The second half of nursing/pumping the milk will turn white and more opaque. This is the fatty part of the milk, the hind-milk. When you store milk, these two layers will separate, which is why you will see a layer of white (the fatty milk) on top of the yellowish-clearish milk. As you continue to nurse, your milk will keep changing to keep up with the nutritional needs of your baby.
Just make sure that you are completely emptying out your breasts when you pump & nurse. That way baby is sure to get BOTH parts of your milk. A lot of times, moms make the mistake of not emptying all the way, then the baby doesn't get the hind-milk.
Are you starting out "fresh" when you pump? Or are you pumping after baby nurses? If you were to pump after nursing you'd have more of the white hind-milk in the bottle and less of the watery fore-milk. I used to nurse on one side, then pump on the other. That way both sides were empty and I was sure our daughter got both parts of the breastmilk.
If you haven't already, check out http://www.KellyMom.com - it's an excellent resource with tons of info for breastfeeding moms.