Each React Native component can take a style prop. You can pass it a JavaScript object with CSS-style style properties:

<Text style={{color:'red'}}>Red text</Text>

This can be inefficient as it has to recreate the object each time the component is rendered. Using a stylesheet is preferred.

import React, { Component } from 'react';
import { View, Text, StyleSheet } from 'react-native';

const styles = StyleSheet.create({
    red: {
        color: 'red'
    },
    big: {
        fontSize: 30
    }
});

class Example extends Component {
    render() {
        return (
            <View>
                <Text style={styles.red}>Red</Text>
                <Text style={styles.big}>Big</Text>
            </View>
        );
    }
}

StyleSheet.create() returns an object where the values are numbers. React Native knows to convert these numeric IDs into the correct style object.

You can pass an array to the style prop to apply multiple styles. When there is a conflict, the last one in the list takes precedence.

import React, { Component } from 'react';
import { View, Text, StyleSheet } from 'react-native';

const styles = StyleSheet.create({
    red: {
        color: 'red'
    },
    greenUnderline: {
        color: 'green',
        textDecoration: 'underline'
    },
    big: {
        fontSize: 30
    }
});

class Example extends Component {
    render() {
        return (
            <View>
                <Text style={[styles.red, styles.big]}>Big red</Text>
                <Text style={[styles.red, styles.greenUnderline]}>Green underline</Text>
                <Text style={[styles.greenUnderline, styles.red]}>Red underline</Text>
                <Text style={[styles.greenUnderline, styles.red, styles.big]}>Big red underline</Text>
                <Text style={[styles.big, {color:'yellow'}]}>Big yellow</Text>
            </View>
        );
    }
}

<View style={[(this.props.isTrue) ? styles.bgcolorBlack : styles.bgColorWhite]}>

If the value of isTrue is true then it will have black background color otherwise white.