Great concept! However my mind started already coming up with ideas how to circumvent this like printing out a color picture of grass! Hope you can detect these fake attempts! :)
But then, the purpose is less about going out and touching grass physically, and more about being aware of what you're spending your time on. A moment of self-reflection, if you will, and whether that's you going outside to find some grass or finding where you put your colour picture of grass and turning the lights on to get a good picture of it is by the by.