This lab shows a plane-polarized electromagnetic wave that is traveling in the +z direction. One color is for the electric field vectors and the other color is for the magnetic field vectors. The right-hand rule says that if you point the fingers of your right hand in the direction of the electric field vector at a particular location, and then curl your fingers into the direction of the magnetic field vectors, your thumb should point in the direction of the way the wave is traveling. Using this rule, you should be able to determine which color arrows represent the electric field vectors and which color arrows represent the magnetic field vectors.