How to link your Google calendar to IPhone

Ensure you have a Google account and can view your calendar via the internet (preferably not on your IPhone).  Make a note of your username and password.

Go into the Settings of your Google calendar and ensure you have set to private shares.

 On your mobile phone go to http://m.google.com/sync where you should be able to log into your Google account and select or manage your device(s).  Select the device you wish to sync and you get to the Settings page.  Tick which calendars you wish to sync to your IPhone and ensure your press on the Save button. 

Assuming you are on a fairly recent iOS version (I am currently using 5.1.1) you then need to go into 'Settings' then select 'Mail, Contacts, Calendars'.  Check your existing Accounts but you may need to add a new Account.  Select 'Add Account' and scroll down to 'Other'.  From the Calendars option select 'Add CalDAV account' and entered the settings as below.  It may take a minute or two to verify your information. 

Finally, open the default IPhone calendar app and select Calendars.  Hopefully, you should now be able to select which calendars you wish to view and relate them to the different colour options available.