Here's how you can use a free application to change the iTunes 11 icon from blue to purple, so it will stand out more on the Dock.
2. Download the free CandyBar application and install it on your system.
3. Launch the CandyBar application (you can use this serial number to register CandyBar for free: PPQA-YAMA-E3KP-VHXG-B6AL-L).
4. Click the Update button to get the latest IconData.
5. Click the Change Application Icons button in the left sidebar.
6. Drag the purple iTunes 11 icon and drop it on the iTunes well, then click the Apply button.
7. Relaunch the Dock.
Your iTunes 11 icon will now be purple. This makes it much easier to see on the Dock, especially if it's near the Mac App store icon.