To find objects using a specific color in your InDesign layout, for example an RGB color, follow the steps below. This works with InDesign CS and CS2.
1. Open your Swatches palette.
2. Select the color that you want to search for and convert it into any spot color.
3. In the Window menu select Output Preview > Separations Preview.
4. In the Separations Preview palette turn ON Separations.
5. Turn OFF the CMYK inks, leaving ON the spot color.
6. The objects using the spot color will remain visible in the layout, while the rest of your objects, text, etc, will be invisible.