Blue lead

===Prismacolor===
Sanford Col-Erase (non-photo blue)
This pencil's lead is quite hard and hardly shows up on the paper. Good if you only want faint marks as guidelines and not so much an actual finished drawing. There is an eraser on the end that actually works to a certain degree; only for peace of mind as you don't need to erase the pencil after inking anyway. The pencil is too light to do actual finished or rough outlined drawings. This pencil would work better with a photocopier.
Sanford Col-Erase (light blue)
Although not officially non-photo it does the same as the non-photo (the blue's light enough not to show up in copies) this one puts down a slightly darker line than the col-erase non-photo and it's softness lands in between the Col-erase and Verithin non-photo pencils.
Recommended in the book 'Drawing words and writing pictures' by Jessica Abel and Matt Madden. You can get a much more finished drawing out of the light blue as opposed to the non-photo, best one to draw with for inking.
Sanford Verithin (non-photo blue)
A lot softer than the col-erase non-photo blue and would be better for a more finished drawing approach. Although the Verithin lays down too much of a waxy line and makes inking with a tech pen difficult clogging the pen. May work better with brush or dip pen.
== Why use non-photo blue pencils? ==
# The light blue colour does not show up when scanned and edited correctly in image editing software, such as Photoshop. It also should not show up in a photocopy, although a more sensitive copier may pick it up.
# If the blue doesn't show up then there is no need for erasing,
#*Ever ripped a page erasing lines?
#*Ever gotten sick of the pile of eraser dust at your feet? 
#*Ever dirtied a page from excessive overdrawing?
# The blue pencil doesn't smudge like regular grey lead pencils.
#It looks appealing to the eye.