如何在lit-element中添加基于属性的类？

import { LitElement, html, css } from 'lit-element';

class MyElement extends LitElement {
  static get styles() {
    return css`
      .red {
        color: red;
      }

      .blue {
        color: blue;
      }
    `;
  }

  static get properties() {
    return {
      color: { type: String }
    };
  }

  render() {
    return html`
      <div class="${this.color}">Hello, LitElement!</div>
    `;
  }
}

<my-element color="red"></my-element>
<my-element color="blue"></my-element>