I'm not sure about editing them, but there's a thread in the xda inc2 section that has modified CWM recoveries. There's like six different colors, and he took out all the no's from the option menus (makes it easier to make selections). The OP may help you in making your own modifications. I would think all you have to do is switch out the png files.
A forum community dedicated to Android phone owners and enthusiasts. Come join the discussion about applications, recovery, developments, styles, reviews, accessories, classifieds, and more for Unbuntu, Google Nexus, HTC, Motorola, Samsung or other Android models!