Red and white is the original iCal icon color. Let's change it.
iCal icon is stored in the file
App-empty.icns. This file full-path is :
Macintosh HD ▸ Applications ▸ iCal ▸ Contents ▸ Resources
You are recommended to back up the original icon before doing some changes in the icon. Now, open the App-empty.icns with Preview. Next, you may use the new Preview tools Adjust Color and make the adjustments like below :