 In addition to the typical Yellow Cab vehicles, there is a Green Cab (ecologically green), a few Pink Cabs (to promote breast cancer awareness), a Red Cab (to promote heart health) and a couple Blue Cabs (to promote prostate health).Cabs which bear the designation "METRO" on their tail ends denote probationary cab drivers, who are required to drive Metros until at least one month has passed since the end of their training; the actual amount of time before a new driver may drive a "Yellow" is determined on a case-by-case basis.The main distinction between a "Yellow" and a "Metro" is that Metro drivers are encouraged to learn to work the town, by not being permitted at the airport.