I have worked very hard on my formula (almost 2 years of trial and error in fact!) to ensure that your breast milk stone will not change colour as time goes on given it is properly cared for.  Please visit the Caring for Your Jewelry page for full details on how to care for your breastmilk stone so that it lasts a lifetime. That being said, everyone's milk is a slightly different colour and this may be reflected in the final piece. I have seen many different colours of milk including yellow, white, clear, cream, tan, or blue-tinged. I have even seen pink-ish! That's the miracle of breast milk, and it adds to the uniqueness of your special piece.