The pumpkin varies greatly in form, but is generally oblong or ovoid in shape. The rind is smooth and varies in color between cultivars. Although orange is the most common color, some fruits are dark green, pale green, orange-yellow, white, red and gray. Large specimens acquire a weight of 40 to 80 lb (18 to 36 kg), but smaller fruits are more frequently encountered.
Here is some information I found on the Blue and Red pumpkins for you.
The blue pumpkin is really rare. It is often often referred to as Australian Blue Pumpkins. More closely resembling a Turban squash than a true pumpkin, they are smaller and flatter than a Jack O'Lantern with a bluish grey color.
The best known, yet hard to find red pumpkin variety is the "Rouge D'Etant". There is also a red pumpkin variety called "Cinderella".
Here is a picture of the blue pumpkin:
Also, here is a picture of the red pumpkin. I hope that helps!