A script to randomize all the character colors in a Google Doc. Use with caution.

Colorify.gs

function Multicolor() {
  
  var doc = DocumentApp.getActiveDocument();
  var body = doc.getBody();

  //This  Loops Through All Paragraphs
  for(var i=0; i<body.getNumChildren(); i++) {
    var par = body.getChild(i);
  
  //This Loops Through Paragraph Children
    for(var y=0; y<par.getNumChildren(); y++) {      
      var txt = par.asParagraph().getChild(y);
      var len = txt.asText().getText().length;
      Logger.log(y);
    //This Loops Through Text Within Each Paragraph
      for(var x=0; x< len; x++) {
        var randomR = Math.round((Math.random() * 255));
        var randomG = Math.round((Math.random() * 255));
        var randomB = Math.round((Math.random() * 255)); 
        
        string = txt.asText().getText().charAt(x);
        
        rgbHex = rgbToHex(randomR, randomG, randomB);
        
        txt.asText().setForegroundColor(x,x,rgbHex);  
      };
    };
  };
}