This is probably more information then you want to know about fingernails but it will help in answering your question. Our fingernails are basically made up of a hard, curved plate of keratin. Keratin is a protein and it is also what makes up hair and the outer most layer of skin. At the base of a nail is what is called the matrix. The matrix is where the nail forms from; this is what most people call "the moon" of the nail. This "moon" appearance is due to the nail bed being so tightly packed with keratin, that the capillaries (where the blood flows through) is covered by the amount of keratin. The rest of the nail that is actually attached to the skin appears pink due to the capillaries running underneath (the blood running through them gives them the pink color). Nails that extend beyond the tip of the finger are white in color because there is no pigment in the nail to give it color.
Nails start in the nail bed, a flat surface that is under your nails and extends about inch beyond where you can see them. When cells at the root of the nail bed grow together to form keratin, a nail is formed. Layers of keratin bind together and the nail slowly grow out from the root of the nail bed towards the end of your finger. Nails grow very slowly. The nails you see now will not be fully replaced by entirely new nails until 6 months or more from now.
White spots on the nails are very common and usually recur. These small, semi-circular spots result from injury to the base (matrix) of the nail, where nail cells are produced or imperfections when the nail is formed. As the nail grows these blemishes are pushed outward. Frequently the culprit of these spots is careless manicuring. These spots are not cause for concern and will eventually grow out.
Another leading cause of these white specs is a diet that is deficient in zinc. You could try taking a zinc supplement and see if this clears up the problem.
Sorry for being a little long winded. But FX hope this answers your question.