Answer:
I usually wear a yellow coat. I usually have a dark head. I make marks wherever I go.
Always old, sometimes new. Never sad, sometimes blue. Never empty, sometimes full. Never pushes, always pulls.
I pass before the sun, but make no shadow.
What do you have when you're sitting down that you don't have when you're standing up?
What goes through a door but never goes in. And never comes out?
What did the piece of wood say when he saw the screwdriver and screws approaching?