You have to create extra calendars. You can not do this on the iPad. Instead you need to sync it with an online service, or your computer, and create the calendars there.
I recommend Google as an online solution. It is free, and not too difficult to set up. You also get the option of doing things in a browser.
When you create a Google account with email, you automatically get a calendar account too. You go there and set up as many calendars as you want, and name them what you want.
Then you set up your iPad. You'll want to use this alternate method to set up the account, instead of the default GMail one. Otherwise you only get one calendar.
Setting up Google Sync with your iOS device : Google Sync (ActiveSync) - Google Mobile Help
When the popup comes up asking what to do with calendar events, choose Merge (think that's what it offers). Whatever you do, do not choose delete or overwrite. Better to have double events you need to remove than lose them all.
After you've done this, go to m.google.com/sync in Safari on your iPad. You'll need to log in with your new Google account. Once you do select your iPad from the list and then select the calendars you want to sync.
The first time you open the Calendar app it might take a while for the calendars to appear. If they don't tap on the Calendar button to the left and see if they are all there, and checked as visible.
The colors don't always match the online colors. Sometimes they do, and sometimes they do then change later. I have no idea why or how to prevent it, but each calendar should have it's own unique color.