TextInput underline color for ios in react-native

You could add borderBottomWidth and borderBottomColor to TextInput or simply draw a view with 1 or 2 px height below TextInput.

Try this in styles.. see the difference in output

const styles = StyleSheet.create({

    inputBox: {
        .....
        borderBottomWidth: 1,
        borderBottomColor: 'gray',
        ....
    }
});

Finally add the style in textInput

<TextInput
 ...             
 keyboardType = 'numeric'
 placeholder = 'Batch Number'
 autoCapitalize = 'none'
 style={styles.inputBox}
.....                                                    
/>