/* Text Higlight Color /**/
  :root {
    --highlight-color: null;
  }

  ::selection {
    background: var(--highlight-color);
    color:#FFFFFF;
  }
  ::-moz-selection { /* Code for Firefox */
    color: #FFFFFF;
    background: var(--highlight-color);
  }
  </style>

  <!-- Text Highlight -->
  <script>
    const colors = ["#F76808", "#30A46C", "#0091FF", "#6E56CF", "#E5484D"];
    window.addEventListener("mousedown", (e) => {
      const color = colors.shift();
      document.documentElement.style.setProperty("--highlight-color", color);
      colors.push(color);
    });
  </script>

Sad, because it sounded interesting, but no way I could focus enough to actually comprehend it.