I have a paper box of Prismacolor coloured pencils. I avoid using them since I think my drawing doesn't deserve them. The odd time I do use them and make mistakes I have a hard time erasing them.
After looking at their FAQ I realize this is the nature of the beast:
Q: Why is it so hard to erase a Prismacolor colored pencil?
A: The Premier Soft Core and Premier Verithin® Colored Pencils are wax based pencils, thus they are not designed to be erased easily. If you’re looking for a medium that is designed to be erased, try out Col-Erase® Colored Pencils and erase away!
What erasers or corrective tools can I use with wax coloured pencils?