Shaderblow oldfilmfilter: how to transition to the original colors

I am looking at the shaderblow examples and I found the OldFilmFilter where you can change some parameters of the filter. You can change the color density which will change the predefined color to gray and back. I also looked at the ColorScale example where you can overlay the scene (as in the oldfilmfilter) with a red layer. The intensity of this red layer can also be changed. The difference between these two examples is that in the oldfilmfilter you change between the predefined color and gray, and in the colorscale example between a predefined color and the normal scene (like when the filter is removed. My question is now, how can I change this oldfilmfilter example so that it won’t transition from the predefined color layer to gray , but to the normal colors of the scene (like when there is no filter).