The free trial lets you use ColorArt Deluxe for one week at no cost. At the end of the week, it will renew at the normal weekly subscription price of $2.99 USD, or equal to the same price tier that “Apple’s App Store Matrix” determines in other currencies, charged every 7 days to your iTunes Account.
If you are unhappy, you can end your subscription by turning off automatic renewal in the Settings app. To avoid the first renewal charge, you must turn off automatic renewal at least 24 hours before the free trial period ends. See How do I stop or change my subscription.