Color depends on the type of pearl. Most unusual colors are more expensive. Tahitian or black pearls are from the Pacific Islands particularly French Polynesia. South Sea pearls come from Indonesia and Philippines for white colors. Color is a matter of preference.
Size the larger sizes are usually more expensive.
Shape is important. An ideal pearl is perfectly round.
Surface Condition The pearl should be smooth and free of pits, holes, scratches and imperfections. Some are acceptable though in natural and larger pearls.
Pearls are extremely delicate, organic pieces. They require proper care. Store them separately in cloth lined boxes or jewelry bags.
Never wear your pearls in a swimming pool. And keep hair products, cosmetics and perfume away. Put your pearls on last after your products have dried. Wipe any residue off with a soft dry cloth.
Restring your pearls every five years. More often if you wear them regularly.