First, take your clock apart to this state:
There is some polarizing plastic that is stuck to the glass display. You need to peel that off and remove the sticky stuff from the back. Then, you flip that piece to make the back face front. You will see the display change colors from dark to light.
Next, you get some plastic that is translucent and blue (tidy cat, multiple cat forumula jug lid, flattened) and make a replica of the white back piece:
Then, you remove the bulb and take off the green rubber cap.
Put it all back together and you get an "indiglo" look.
Or you can just send it to me and I'll do it for $15.