Hey, I helped edit that book! (I think my name is in the acknowledgements, and he the author even references Muvipix.com, the Premiere Elements support site I helped create, in the book.)
But if you really want to know how to use these effects, you should get MY books! I show you how to create AND fine-tune the effects.
Most likely what you're seeing is the result of the effect's default setting.
Just right-click on the clip that you've applied Videomerge to and select Show Properties. This will open the clip's Properties panel.
Locate and open the Videomerge properties. Adjusting the slider should fine-tune the effect.
already ordered the book. eagerly waiting for..
Now I already played with the options, The tolerance slider was not helpful, the green disapeared, but the grey came in some rather bigger parts. Its like a grey shade, cant get it away with chroma key either if applied to the track afterwards
You can try applying the Chroma Key or the Green Screen Key first -- or instead. And you can try applying Auto Color before you apply the keys.
I'm not sure why the Videomerge engine functions differently in version 9 than version 7, but the principles of all key effects is the same. You designate the color to be keyed, and you adjust the range of that color to be affected.
Some key effects work better than anothers in any given situation.