I have written a tutorial for Adobe Photoshop on how to leave a selected color in a photo that turns greyscale. Here is the equivalent of that for Adobe Premiere 2.0. Adobe Premiere actually has a filter named "Leave Color" - hense the title of the tutorial, which Adobe Photoshop does not have (although I think it should).
1. Preparing the clips
First import the filmed material into Adobe Premiere and put the chosen clips into the timeline. I have chosen a few clips of our cat and added some nice Debussy music.
2. Leave color effect
Select the Leave Color effect, which is located under Video Effects -> Stylize -> Leave color.
3. Parameters
Set the parameters so that one color you desire will stay and others will go greyscale. Set Amount to Decolor to 100%. Be careful when picking the Color To Leave and experiment a little. I decided to leave the color of the cat's fur. when I selected the exsact color of the cat's fur I couldn't leave it without the green of the grass. I asume this happend because brown and green are close together on the color scale and when I set tolerance to 50% the green came in. The solution here was to select pink. When you find the right color play with the tolerance until you get the desired effect.
Here is the result of the Leave Color effect:
You can download the movie of the cat with the Leave Color effect by clicking on the download button below or watch it here.