Rich ReactNative TextInput

You will have to use regex in order to achieve that behaviour. Someone has already created package for that have a look at react-native-parsed-text

This library allows you to parse a text and extract parts using a RegExp or predefined patterns. Currently there are 3 predefined types: url, phone and email.

Example from their github

<ParsedText
          style={styles.text}
          parse={
            [
              {type: 'url',                       style: styles.url, onPress: this.handleUrlPress},
              {type: 'phone',                     style: styles.phone, onPress: this.handlePhonePress},
              {type: 'email',                     style: styles.email, onPress: this.handleEmailPress},
              {pattern: /Bob|David/,              style: styles.name, onPress: this.handleNamePress},
              {pattern: /\[(@[^:]+):([^\]]+)\]/i, style: styles.username, onPress: this.handleNamePress, renderText: this.renderText},
              {pattern: /42/,                     style: styles.magicNumber},
              {pattern: /#(\w+)/,                 style: styles.hashTag},
            ]
          }
        >
          Hello this is an example of the ParsedText, links like http://www.google.com or http://www.facebook.com are clickable and phone number 444-555-6666 can call too.
          But you can also do more with this package, for example Bob will change style and David too. [email protected]
          And the magic number is 42!
          #react #react-native
</ParsedText>

Solution is that you can use <Text> elements as children in a <TextInput> like this:

<TextInput>
    whoa no way <Text style={{color:'red'}}>rawr</Text>
</TextInput>

This question was asked a while ago but I think my answer can help other people looking for how to color the @mention part of a string. I am not sure if the way I did it is clean or the "react" way but here is how I did it: I take the inputed string and split it with an empty space as the separator. I then loop through the array and if the current item matches the pattern of @mention/@user, it is replaced with the Text tag with the styles applied; else return the item. At the end, I render inputText array (contains strings and jsx elements)inside the TextInput element. Hope this helps!

render() {
let inputText = this.state.content;
if (inputText){
  inputText = inputText.split(/(\s)/g).map((item, i) => {
    if (/@[a-zA-Z0-9]+/g.test(item)){
      return <Text key={i} style={{color: 'green'}}>{item}</Text>;
    } 
    return item;
  })
return <TextInput>{inputText}</TextInput>

Have a look at the TokenizedTextExample from the react-native docs. I think that'll get you close to what you're looking to do. The relevant code follows:

class TokenizedTextExample extends React.Component {
  state: any;

  constructor(props) {
    super(props);
    this.state = {text: 'Hello #World'};
  }
  render() {

    //define delimiter
    let delimiter = /\s+/;

    //split string
    let _text = this.state.text;
    let token, index, parts = [];
    while (_text) {
      delimiter.lastIndex = 0;
      token = delimiter.exec(_text);
      if (token === null) {
        break;
      }
      index = token.index;
      if (token[0].length === 0) {
        index = 1;
      }
      parts.push(_text.substr(0, index));
      parts.push(token[0]);
      index = index + token[0].length;
      _text = _text.slice(index);
    }
    parts.push(_text);

    //highlight hashtags
    parts = parts.map((text) => {
      if (/^#/.test(text)) {
        return <Text key={text} style={styles.hashtag}>{text}</Text>;
      } else {
        return text;
      }
    });

    return (
      <View>
        <TextInput
          multiline={true}
          style={styles.multiline}
          onChangeText={(text) => {
            this.setState({text});
          }}>
          <Text>{parts}</Text>
        </TextInput>
      </View>
    );
  }
}