And that tells us that the antibody is present inside that sample. Because if the antibody was not present in our sample, then following that washing process, we basically would remove any antibody that was not bound. And if that blue antibody was not bound to a red antigen, then we essentially remove everything that was present in our mixture, including these green antibodies that contain the enzyme. And so following the washing process, if we add the substrate because no enzyme is present in that mixture, the color change would not actually take place. So the color change signifies the presence of that antibody that we are actually searching for in the first place. Now, the darker that color change is, the higher the concentration of that antibody inside our mixture.