Most of us hook up our Google accounts with our iOS devices using Exchange, which pushes new mail to your iPhone. But if you sync Google Calendar using Exchange, your calendar colours don't sync. Luckily they can, and there's a simple solution.
Lifehacker reader njefferson shared a tip pointing out that if you set up your Google Calendar to sync using CalDAV, the calendar colours sync seamlessly between your iOS device and Google Calendar. If you add a calendar or change a calendar colour on Gcal, the colours will sync to your device. Just turn off calendar sync on your Exchange account, and enable it via CalDAV.
On iOS 4+ devices, you can skip the CalDAV setup and just use the default Gmail account setup option in the Settings app to sync with Gcal. (The iOS 4 update hasn't made it's way to the iPad yet, so iPad users will need to use the CalDAV method for now.)
After switching to CalDAV, colour syncing hasn't worked perfectly on all of my calendars (it seems like it may be a shared calendar problem), but where it doesn't work at all via Exchange, it works with most of my calendars using the CalDAV or Gmail account methods.