Because pigma pens use pigment based ink and not dye based ink, they do not fade, the colors are consistent and they do not bleed. I get mine from Dick Blick, an art supply store. They aren't the cheapest, but they have the widest variety...15 colors and 6 point sizes (I get way too much stuff there :oops: ).
http://www.dickblick.com/products/sa...ma-micron-pen/