Look around for a pen with mulitple colours in the barrel many have at least four I've come acoss some with 8. Eight colours is quite suffient 4 or five will do too. consider black, red, blue and green, the standard in pens you can add either a highlighter type for a 5 colour and you're set.
When it comes to erasing... it shouldn't really be necessary. Just draw arrows to link it to correct sections.
I find I work my mind maps in a clockwise fashion starting at 1 o'clock. From there when the topic changes to a diffent core Idea i move clockwise. I find that on a mind map about 6 main branches works really well. Then I use another sheet of paper since it can start getting crowded.
Alex
