Contact Canon and purchase an extra O ring
Learn to use the manual hue settings. See my blog in educational section
If this is a new on the market piece of equipment, purchase product/equipment insurance for your camera and housing. Older gear isn`t worth the insurance since you can pick up replacements on Ebay for next to nothing.
Learn the maintenance. Removal, cleaning, and reinstalling the O ring is a life or death scenario for a camera. It only takes a single hair to cause a leak. So, it is absolutely important that the O ring be removed from the housing and cleaned when the camera is removed. DO NOT relube the O ring or replace it in the housing until you are ready to use the housing again.
Dry-absorb packets you find with factory packaged electronics are a wonderous thing to have in your housing. If you get just a tiny bit of moisture inside (usually causes fogging inside), one of these should take care of the problem.
Share your shots when you can.