Huey PRO Colorimeter
Select ThinkPads feature a Pantone Huey PRO Colorimeter by X-Rite in the palm rest. This is used for calibrating the colours of the LCD display. The way calibration works is that you close the LID and the display remains on with a special test screen, and the sensor in the palm rest does its thing.
If you do not have a colour meter, Lenovo provides pre-calibrated profiles for most ThinkPads. Please see Colour profile.
Linux support
Help needed
If you have a ThinkPad with this sensor and have gotten it to work, please update the instructions
This sensor may work with argyllcms. If it does it should also work with gnome-color-manager which is included with newer distributions like Fedora 13.