معما

RIDDLE ME THIS: 

For some I go fast
for others I'm slow.
To most people, I'm an obsession
relying on me is a well practiced lesson.

 What am I? 
  time  A blue house is made of blue bricks. A yellow house is made of yellow bricks. A red house is made of red bricks. An orange house is made of orange bricks. What would a green house be made of?  Glass  http://riddles.com/