Get filtered/non-filtered values from Google Sheet with Google Apps Script

Code.gs

/**
 * Get values in range
 *
 * @param {String} rangeA1 The range in A1 notation
 *
 * @return {Array} array with non-filtered values
 */
function getValues (rangeA1) {

  // Get range
  var range = SpreadsheetApp.getActiveSheet().getRange(rangeA1);

  // Get values
  var values = range.getValues();
  
  // Prepare an array for the non-filtered values.
  var v = [];
  
  // Get the font color of each cell in our range.
  var oldColors = range.getFontColors();
  
  // Create a new array with different font colors.
  var colors = [];
  for (var r = 0; r < oldColors.length; r++) {
    
    colors[r] = oldColors[r].slice(0);
    
    // Modify the color slightly from black
    // (I figure that's the most common color)
    for (var c = 0; c < colors[r].length; c++) {
      colors[r][c] = (oldColors[r][c] == '#000001') ? '#000002' : '#000001';
    }
  }
  
  // Set the font colors to the generated colors.
  range.setFontColors(colors);
  
  // Get the font colors at this point.
  // They should have changed. If they haven't that means
  // the cell was filtered!
  var newColors = range.getFontColors();
  
  // Check filter status cell for cell
  for (var r = 0; r < colors.length; r++) {
    for (var c = 0; c < colors[r].length; c++) {

      // Store the value if it wasn't filtered
      if ((oldColors[r][c] != newColors[r][c])) {
        v.push(values[r][c]);
      }

    }
  }
  
  // Change the background colors back to what they were initially
  range.setFontColors(oldColors);
  
  return v;
}

This grabs the values and puts them in an array, but it should be quite easy to modify the code for other purposes.