My sole edges are nearly black and the heels are dark shades of brown. It's got to be due to the differences in how and where they're worn. I remember when mine were new the sole edge coloring wore off extremely fast. A little boot oil and they darkened back up and then just got darker from there.
Well yes, that would happen - but using the light wood stain not only makes the edge look good (more original), but it really protects the edge and doesn't wear off easily.