Mixture is a beautiful theme that offers you the possibility to quickly give a colorful look to your iTunes.
To install the Mixture iTunes theme navigate to your iTunes application, press right click and choose Contents from the contextual menu. In the Resources folder you will be able to find the iTunes.rsrc file.
Backup the file in case you want to restore the default theme and then place the .rsrc file included in the Mixture package in the Resources folder. When you launch iTunes you will be able to see the new theme.