I would think that they're not ripe yet and like most fruits will turn from green to the colour they should be when they are ripe and ready to harvest.

Thanks for reply! Someone had suggested the pumpkin I took seeds from may of been cross pollinated when grown originally! So was wondering if his was a throw back or some type of cross? Sorry for my ignorance but used to just growing peppers and chilli,s :-)

That's right. The seeds you took could be from a hybrid Pumpkin. If that's the case then yours probably won't come true and will revert back to the mother or father plant that created the hybrid, or as you said, would be a throw-back.

The other thing that could happen is the Pumpkins that you are growing could have been cross-pollinated. For example, this could happen if a bee visited say a Squash plant, Gourd plant, etc, before yours. The bee would carry pollen from the male flower and pollinate your (female) flower. You could end up with something interesting though, something nice, or something weird like crossing an Alsatian with a Poodle ;o)

Cut off the leaves covering the pumpkins to let the sunlight get to them now and keep watering and feeding. Pumpkins go lighter as they ripen but need light on the fruit.

Thanks for the comments! :-)