Using Context and ShouldComponentUpdate

Themes.js

class ThemeProvider extends React.Component {
  constructor(p, c) {
    super(p, c)
    
    this.getColor = this.getColor.bind(this)
  }
  
  getColor(){
    return this.props.color //could be this.state.color
  }

  getChildContext() {
    return {getColor: this.getColor}
  }

  render() {
    return <div>{this.props.children}</div>
  }
}
ThemeProvider.childContextTypes = {
  getColor: React.PropTypes.func
}

class ThemedText extends React.Component {
  render() {
    return <div style={{color: this.context.getColor()}}>
      {this.props.children}
    </div>
  }
}
ThemedText.contextTypes = {
  getColor: React.PropTypes.func
}