The numbers tell the reader, this was that number of baby wearing that size of band, hatched at TreeTop Aviaries. This number is used by most aviaries as a way of recording keeping. I record who purchased the baby and when the baby was purchased. For quick reference the hatch dates and parents are recorded on the same sheet. Color is another identifier of the a band.
Some breeders use a different color for each calander year.
At TreeTop we only use red leg bands. I cant tell you why, I just like the color red. The bands used at TreeTop also have a year imprinted on the band. It is a way of knowing when the baby was hatched. In this case 00 means 2000.