I had shot a video with just a lighting on the foreground (and not on the background). The end result was that the green screen had uneven shades. Keying it out was difficult.
Then, I tried to “blow-up” the greens using Technocolor — and that did it! I mean, that instantly keyed out the green background using Chroma: Simple. Then, I reverted back the color using Technocolor with a minimal setting.