User interface for chroma keying (green/blue screen compositing)
Submitted by Jeff F.T.
We need a reusable user interface for picking a color value from the viewer and applying it to the properties of an effect being configured. This will make chroma keying much easier.
For example while configuring the White Balance effect applied to a clip, it would be very useful to be able to pick a grey point from the viewer as the "white". Similarly with the color which becomes transparent in Bluescreen0R, etc. See https://docs.google.com/document/d/17P7lSjTaFqyYWZV2NGqBZ_czDA0TvWNPOBQHi6ypFa8 for more examples.
Imported from https://bugzilla.gnome.org/show_bug.cgi?id=634946