Spraying hairspray and other decorative sprays over carved pumpkins will keep them from turning brown. They will also help keep them from drying out. Spraying it about every four days with a mixture of warm water and bleach will keep it fresh. It will also prevent mold from growing.
Spraying hairspray on your pumpkin will preserve it as you would like to keep your hairstyle. It is also said to repel pests. You can spray on the inside and outside of a carved pumpkin as well.
Coating the insides of pumpkins and on cutting surfaces with a sealing agent (like Vaseline) helps keep the flesh of the pumpkin from drying out.