How Can I access the developer menu on device ou emulator?
You can access the developer menu by shaking your device or by selecting "Shake Gesture" inside the Hardware menu in the iOS Simulator. You can also use the ⌘D keyboard shortcut when your app is running in the iOS Simulator, or ⌘M when running in an Android emulator on Mac OS and Ctrl+M on Windows and Linux. Alternatively for Android
How to customize components of NativeBase?
NativeBase provides a separate file inclusive of color schemes for all components.
Go through Customize section of docs.