Non Photo Blue/Non Repro Blue

I've finally found out what those blue pencils are called. The ones that are untracable to photocopiers and scanners... They're called non photo blue pencils. Repeat, non photo blue pencils. Now when you walk into your art supply shop, you can ask for them and not just "a blue pencil". Its the pencils animators, designers and comic book pencilers use. You don't need to rub them out, you can just ink over them and whamo they're untracable when scanned. Any old blue pencil doesn't work, it must be a certain blue that the copier can't pick up...