Can I color certain words in Google Document using Google Apps Script?

With the introduction of document-bound scripts, it's now possible to make a text highlighting function that's invoked from a custom menu.

Surely THIS is the best answer now! 8^)

This script was modified from the one in this answer, and may be called from the UI (with no parameters) or a script.

/**
 * Find all matches of target text in current document, and highlight them.
 *
 * @param {String} target     (Optional) The text or regex to search for. 
 *                            See Body.findText() for details.
 * @param {String} background (Optional) The desired highlight color.
 *                            A default orange is provided.
 */
function highlightText(target,background) {
  // If no search parameter was provided, ask for one
  if (arguments.length == 0) {
    var ui = DocumentApp.getUi();
    var result = ui.prompt('Text Highlighter',
      'Enter text to highlight:', ui.ButtonSet.OK_CANCEL);
    // Exit if user hit Cancel.
    if (result.getSelectedButton() !== ui.Button.OK) return;
    // else
    target = result.getResponseText();
  }
  var background = background || '#F3E2A9';  // default color is light orangish.
  var doc = DocumentApp.getActiveDocument();
  var bodyElement = DocumentApp.getActiveDocument().getBody();
  var searchResult = bodyElement.findText(target);

  while (searchResult !== null) {
    var thisElement = searchResult.getElement();
    var thisElementText = thisElement.asText();

    //Logger.log(url);
    thisElementText.setBackgroundColor(searchResult.getStartOffset(), searchResult.getEndOffsetInclusive(),background);

    // search for next match
    searchResult = bodyElement.findText(target, searchResult);
  }
}

/**
 * Create custom menu when document is opened.
 */
function onOpen() {
  DocumentApp.getUi().createMenu('Custom')
      .addItem('Text Highlighter', 'highlightText')

      .addToUi();
}

I think it's possible with the method setBackgroundColor of class Text in DocumentApp : https://developers.google.com/apps-script/class_text#setBackgroundColor

You'll have to retrieve your words as Text elements. In order to do that you can use the find method of your object Document, then to iterate over the search results and use getElement. Finally, to convert your Element object into a Text object, you can use asText().

Hope it'll work ! ;)

This is a better solution:

function highlightTextTwo() {
  var doc  = DocumentApp.openById('<your document id');
  var textToHighlight = 'dusty death';
  var highlightStyle = {};
  highlightStyle[DocumentApp.Attribute.FOREGROUND_COLOR] = '#FF0000';
  var paras = doc.getParagraphs();
  var textLocation = {};
  var i;

  for (i=0; i<paras.length; ++i) {
    textLocation = paras[i].findText(textToHighlight);
    if (textLocation != null && textLocation.getStartOffset() != -1) {
      textLocation.getElement().setAttributes(textLocation.getStartOffset(),textLocation.getEndOffsetInclusive(), highlightStyle);
    }
  }
}

Previous Answer:

The key is to being able to reference just the words you want to color.

My solution is to:

Get the text of the paragraph that contains the words you wish to color, remove the original paragraph, then add each part of the text back. As you add each part back the appendText returns a reference to just the text added, you then can specify its color with setForegroundColor():

function highlightText() {
  var doc = DocumentApp.openById('<your document id>');
  var textToHighlight = 'dusty death';
  var textLength = textToHighlight.length;
  var paras = doc.getParagraphs();
  var paraText = '';
  var start;
  for (var i=0; i<paras.length; ++i) {
    paraText = paras[i].getText();
    start = paraText.indexOf(textToHighlight);
    if (start >= 0) {
      var preText = paraText.substr(0, start);
      var text = paraText.substr(start, textLength);
      var postText = paraText.substr(start + textLength, paraText.length);
      doc.removeChild(paras[i]);
      var newPara = doc.insertParagraph(i, preText);
      newPara.appendText(text).setForegroundColor('#FF0000');
      newPara.appendText(postText).setForegroundColor('#000000');
    }
  }
}