Lentils do come in different color varieties. The typical grocery store usually only carries one kindd. But if you go to a HFS or Whole Foods or Wild Oats, you can find the lentils in red, green, black... I get the red lentils in the bulk bins at Whole Foods or Wild Oats.
Incidently, red lentils are suppose to be the easiest type of lentil to digest, so it's a good one to start with.