There are a number of ways to do it. By far the easiest, if you have it, is to use the NewBlueFX (which came with SVMS V08). Not in front of SVMS now, but have a look at newbluefx.com for the actual effect name.

Also do a quick internet search as there are tutorials on other approaches (which may be free)

This is generally called the "Pleasantville Effect" (from a movie that used it). You might try searches using that term.

In Vegas Pro it can be done with the Secondary Color Corrector filter, which I believe is not available in Vegas Movie Studio or Movie Studio Platinum.

Sounds like NewBlueFX must have something available to help with this. Otherwise, you *might* be able to do it as follows (but I've never tried it):

1. Put the video on two tracks, one above the other.

The lower track will be the version that keeps the color. The upper track will be black-and-white with a "hole" where needed to let the desired color part of the lower track show through.

2. On the upper track, apply the Chromakey effect and select the color you want to keep. Adjust to get a good negative "mask" of the color you plan to keep -- mask is white where you want B&W result, black (transparent) where you want color result (where lower track will show through).

3. Once that is set, apply B&W effect to the upper track, making sure it is *after* the chromakey.

Like I said, I've never actually tried it -- might not produce satisfactory results. NewBlue might be a better approach.

Tim L