Some breed standards require dewclaws to remain intact so check with your veterinarian or breeder if you are planning to show your dog. If your dog has all his nails, all of them need to be maintained. Dewclaws can be surgically removed on an older dog but the operation requires general anesthesia and can be quite painful and expensive. The nail consists of an epidermis, or outer layer which is what we see. It can range in color from an opaque black to essentially transparent.
Some dogs have nails of different colors.
Within the epidermis is the dermis or quick which is shown here in pink. The quick has blood vessels and nerve endings. When cutting nails, it is essential to avoid cutting into the quick. Even though it can make your dog uncomfortable, cutting just the tip of the epidermis does not cause any pain. However, cutting into the quick will cause the nail to bleed and your dog will likely squeal in pain and run away.