You can create different colored calendars in the native app.
Tap the Calendar button at the top left, then tap Edit. Tap Add Calendar to create a new on, then choose your color. Or tap an existing calendar to change its color. You're limited to 7 choices of colors, but that is usually enough.
When you are creating or editing an entry you will be able to choose/change the calendar. In Settings > Mail, Contacts, Calendars; under the Calendar settings you can specify what calendar you want us use by default.
If you are not already doing so, I recommend keeping your calendars synced with an online service like. iCloud or GMail. If you have nothing now, iCloud is the easiest setup and most versatile. If you already have a Google account you can use it, but will need to
change your account type to Exchange, and go through a couple extra steps to sync multiple calendars.
My biggest reason for recommending this is so that you can recover you calendar data in case something happens to the iPad or a gremlin takes a swipe at the app. Happens.