I also agree about the dangers of using the colored belt system. I enjoyed it during my TKD years as a teenager; my youngest brother and I were stupidly competitive about the belts. But when he quit (from boredom, I think?), it diminished the thrill of getting another belt for me. Not only that, the master instructor kept adding belts. It was nine ranks to 1st degree blackbelt when I first joined, and when I left, the number of ranks to black grew to *fifteen*. Two of those ranks were added when I was two ranks from black - and those ranks (called "Deputy Blackbelt...huh?!) happened to be above my current rank. And on top of the added belts, he cut down the classes from 1.5 hours to one hour. I was NOT happy with both of those developments and left (I was a "Deputy Blackbelt" at the time).
Belts will only motivate a child or teenager for a short amount of time. There needs to be some kind of substance in the training too. I quit that dojang because even at a young age, I saw the lack of substance behind the many colored belt ranks. Not to mention a LOT of mediocre kiddie blackbelts.
Makes me appreciate the white belt/black belt system even more.