Even though the Bluefruit Connect app only uses UART as the transport for sending and receiving data to/from your BLE device, it has multiple interaction modes
Each of these modes can do different things and let you interact in a unique way.
Don't forget! All of these modes use the UART Service, but present the data in a different way. On the hardware side, your firmware will have to know what it is expecting and sometimes may need to parse the data coming back from the app.
For example, if using the Color Picker, the app will send the color data in a mini packet. If using the button controller, you'll get button presses/releases in packets instead.