Color Accent is a feature found in some Canon Powershot point-and-shoot cameras. Not all Powershots have it. To be sure, ask the seller first before paying.
Extract Color is also a feature of the Pentax K-x dSLR.
Basically, you select what color to preserve. The rest are transformed into B/W. In the K-x, you can do this before or after you take the shot.
Now you know!