Cover the entire pumpkin with gesso in stages. Allow to air dry. (A heat tool will cause the gesso to bubble.)
Be sure that your pumpkin is thoroughly coated. It's okay if the coating itself is uneven. You just want the surface to be primed for the next step.
Now cover your pumpkin with metallic paint. I've used a Prima Metallique paint in Steampunk Copper; it's much thicker than the more inexpensive acrylics. A few streaks of white peeking out are fine.
Using a slightly damp sea sponge, dab your pumpkin with Oxide Ink. You'll have a mottled surface as in the picture. (You don't have to treat the bottom, just the visible part.)
Allow to dry for a few hours, preferably overnight. Spray with Matte Finish, coating thoroughly. BE SURE TO DO THIS IN A WELL-VENTILATED AREA. I took mine outside for this step.
Grab some burlap, ribbons, leaves to display your pumpkins.
Another view, showing a few of the colors... Happy crafting!