You can modify the colors and sounds in Google Mobile for the iPhone using a hidden easter egg. Here’s how you access it:

1. Access the Settings area of Google Mobile.

2. Scroll to the bottom of the page, then swipe up several times.

3. The Bells and Whistles entry should eventually appear. Tap it to change the Theme Color, Sounds and to turn Live Waveform and Open Links in App to On or Off.

Discovered at: Access Hidden Options in Google Mobile App for iPhone