This banner ad was up when I visited SueBob over at Red Stapler. I like that they're showing how easy touching up those roots can be but if it's:
A. Morning - when you're most sleepy
B. Rush - you're in a hurry
Do you want to put a brush with color on it in the same glass as the brush you're going to insert into your mouth?
You'd feel a difference immediately I'm sure.. but half your teeth would be brown until your roots grew out.