I’ve just discovered something new! I typically like to start my drawings using an erasable blue pencil (a Prismacolor Col-Erase 20044 Blue) and then use a mechanical pencil (Pentel Twist-Erase) to finish the drawing. This process works fine, but I am constantly having to stop and hand sharpen the blue pencil. I have tried to find blue leads to use in my mechanical pencils, but they are all too brittle and not erasable at all.
Then I discovered PaperMate Erasable Color Leads. These are soft leads, fit my mechanical pencils perfectly and work like a charm… AND you can get them at your local WALMART!! …well, you can’t get them at MY local Walmart because I just bought every one they had last night… but you might want to give these a try sometime. I love em.