How to use Chroma Hold Effect?


I use Kdenlive 0.7.4 on Ubuntu Studio 9.04 and have a good time with it.

Today I try to use "Chroma Hold" video effect on a DV clip but it didn't work. I add "Composite" transition and put other DV clip below the clip but no effect appears on my project monitor...

I hope this effect means the so-called "Chroma Key", to hide the area of a color which I indicate.

If kdenlive don't have this effect, would you please tell me it?
If it has, tell me how to use this effect.

No, the Chroma Hold effect turns your video to grayscale, except for one chosen color. The effect you are looking for is called "Blue Screen", and you have to add a composite transition between the clip with the effect and the track below to make it work

Oh, the "Blue Screen" effect is what I seek.
Thanks, j-b-m!