The "White Grapes icon" displays a clean nice image based on the transparency mask used to create this icon. It looks much nicer!
When you want to create icons for either the iPhone tab or tool bar, you have to understand that the icons are rendered off the alpha channel (transparency) of the image, colors do not matter.
- Programming iOS 4 "Tab Bar Item Images" (page 462) by Matt Neuburg
- How to Draw Pixel-Perfect iPhone Toolbar and Tabbar Icons
- Create UITabbar & UIToolbar Icons for iPhone in Illustrator