The other method is to scrub the outer surface of a gourd away after it has completely dried. You should first soak your gourds in a warm solution of bleach water for a few minutes. This is the recommended method for cleaning gourds. You will lose far less gourds this way than you will by green scraping them. The surface of a scrubbed gourd may also be very even-colored, but others may have dark patterns from mildew on their surface.
Some people like to accentuate any dark patterns in their crafts.
If you use color pencils on your gourds you should certainly use a sealant. In the past I have used clear acrylic spray, and spray polyurethane. Polyurethane provides more protection to the drawing, but will yellow with age. Clear acrylic spray will remain clear but provides less protection. I have recently purchased some Deft, Triple Thick Clear Acrylic Spray, and automotive lacquer to experiment with.