Thank you. I watched your video. There is nothing underneath the video on V1. Shotcut does not blend video on V1 with a black blackground. Shotcut does not show transparent areas with a white-and-gray checker board unless you add the Alpha Channel: View filter. Chroma Key works on your green oval because you have the clip on a track above V1 with something below it so you can see something else. Again, what do you want to see when you remove the color? Move the clip with red oval to a higher track and put whatever you want to see under it.