I suppose that you are familiar with the Philips ambilight. Many projects have been made with little. Mike Shatohin, a software engineer from Russian Federation, Krasnodar, made an ambilight for his laptop, which is the best DIY ambilight that i have seen so far. 4 RGB LEDs are mounted on the back side of the screen, and they are controlled with an AVR ATtiny44. A program that stays resident in the task tray analyzes the screen with specific algorithms. Then, it sends the data through a low speed USB to the microcontroller, which activates the LEDs accordingly, giving excellent results. The project (hardware and software) is also uploaded in this link.