I assume that is because of the model you are printing and a bit because of the filament itself. Some layers seem to need more filament (top, bottom layers) then there might be infill and then there is the hollow part. The more filament per layer the faster the color transitions. I assum the darker red band towards the bottom is just part of the filament. If you want the smoothest transition you should print something that has pretty consistent layers like either something solid (infill is okay as long as it isn’t something like adaptive infill) or a vase mode print.