Grass,water,and dirt gave the Earth it's color. Also put this in your report...Did you know that the Earth is made up of seventy-one percent water. Put that in your report and I guaranty your teacher will think you are the brightest person since Albert Einstein.
Colors come from the pigments. Pigments aer in everything (I think...), for instance grass. When you slide/trip/fall on grass, either you or your clothes are stained green. Those are the pigments being "smeared" across you. Sounds a little gross, but it's true. Good luck on your project - hope this helps! :D