With a photocopier, it has to be blue, because of the blue glass plate within the machine itself (which is also what causes red to go "black"). But with a scanner things are a lot more flexible ... A lot of [the hand-drawn elements in] my maps were actually drawn in magenta, orange, blue, green or other colors using markers, for example, precisely for that reason ... it's a snap for Photoshop to suck away or isolate the color.