Use your Mac's display as an ambient light source.
Your iPhone is the remote control.
Your Mac's display is the light source.
You can project full screen colors on your Mac and control the brightness from your iPhone.
Use it as a soft box for photography.
Shoot your subject under colored light.
With a long exposure, mix colors.
Or just use it as a mood light. Light your room in different colors.
The iPhone app is available on the App Store. Just search for "RoomColors" or grab the App Store link from http://codexbit.com/roomcolors
Just open the app on your Mac.
The iPhone will instantly recognize it if they're on the same Wi-Fi network.
No need to mess around with IP addresses or port numbers.
The iPhone and your Macs will recognize themselves and connect automatically.