Get Colors from RenderTexture faster!

Okay, I read a lot and got to the conclusion that OpenGL is faster, or so everybody says. I tried for past few hours, but there seems to be a major problem in my understanding of how this works. I get a color, but it is like random noise, so I must be reading the buffer wrong. Please help!

 [SerializeField] Light displayLight;
     Camera displayCamera;
     [SerializeField] ParticleSystemRenderer particles;
     [SerializeField] int xResolution = 8;
     [SerializeField] int yResolution = 8;
     [SerializeField] Renderer display$$anonymous$$odelRenderer;
     [SerializeField] bool play$$anonymous$$ovie = false;
 
     $$anonymous$$ovieTexture movie;
 
     void Awake(){
         displayCamera = GetComponent<Camera> ();
 
         if (play$$anonymous$$ovie) {
             movie = ($$anonymous$$ovieTexture)display$$anonymous$$odelRenderer.material.GetTexture ("_Emission$$anonymous$$ap");
             movie.loop = true;
             movie.Play ();
         }
 
         displayCamera.aspect = 4f / 3f;
     }
 
     [DllImport("opengl32")]
     public static extern void glReadPixels (int x, int y, int width, int height, int format, int type, IntPtr buffer);
 
     void Update () {
         displayCamera.Render();
     }
 
     const int GL_RGB          = 0x1908;
     const int GL_UNSIGNED_BYTE = 0x1401;
 
     public byte[] destination;
 
     public class ColorBuffer
     {
         int stackpointer = 0;
         float red = 0f;
         float green = 0f;
         float blue = 0f;
 
         public void save(byte input){
             int position = stackpointer % 3;
 
             switch (position) {
             case 0:
                 red += input;
                 break;
             case 1:
                 green += input;
                 break;
             case 2:
                 blue += input;
                 break;
             default:
                 break;
             }
 
             stackpointer++;
         }
 
         public Color load(){
             return new Color (
                 ((red / (stackpointer / 3f)) / 255f),
                 ((green / (stackpointer / 3f)) / 255f),
                 ((blue / (stackpointer / 3f)) / 255f)
             );
         }
     }
 
     void OnPostRender(){
         int size = xResolution * yResolution * 3;
 
         IntPtr buffer = $$anonymous$$arshal.AllocHGlobal (size);
         byte[] bytes = new byte[size];
 
         glReadPixels(0, 0, xResolution, yResolution, GL_RGB, GL_UNSIGNED_BYTE, buffer);
 
         $$anonymous$$arshal.Copy(buffer, bytes, 0, size);  
 
         ColorBuffer cb = new ColorBuffer();
 
         for (int i = 0; i < size; i++)
             cb.save(bytes[i]);
 
         Color newColor = cb.load ();
         displayLight.color = newColor;
 
         Debug.Log("Color: " + 
             newColor.r.ToString("F2") + ", " + 
             newColor.g.ToString("F2") + ", " + 
             newColor.b.ToString("F2") + ", " + 
             newColor.a.ToString("F2"));
 
         $$anonymous$$arshal.FreeHGlobal(buffer);
     }