Answer:
Take one out and scratch my head, I am now black but once was red.
The more holes you cover the lower it goes.
This is rectangular, hollow and has a lid, and where you’ll find it you might wonder, it is just six feet under. What is it?
I turn around once. What is out will not get in. I turn around again. What is in will not get out.
I run around the city, but I never move.
You use it between your head and your toes, the more it works the thinner it grows.