Apply multiple font colors to the text in a single Google Sheets cell

Question

I am trying to format a cell to have multiple font colors using a function in Google Apps Script. I am unable to find any documentation on it. Also, using getFontColor() doesn't return anything useful.

Is there any way to programmatically reproduce this functionality

that is available to users via the Google Sheets web UI?

Answer 1

The Sheets API is a bit daunting to start using, but allows very fine-grained control over your spreadsheets. You'll have to enable it, as it is an "Advanced Service". I strongly recommend reviewing the Sample Codelab.

With the Sheets API, the TextFormatRun property can be manipulated on a cell-by-cell basis. Note:

Runs of rich text applied to subsections of the cell. Runs are only valid on user entered strings, not formulas, bools, or numbers. Runs start at specific indexes in the text and continue until the next run. Properties of a run will continue unless explicitly changed in a subsequent run (and properties of the first run will continue the properties of the cell unless explicitly changed).

When writing, the new runs will overwrite any prior runs. When writing a new userEnteredValue, previous runs will be erased.

This example uses it to adjust the green value of text, increasing from 0 to 100% over the length of a string in the active cell. Adjust to suit your needs.

function textFormatter() {
  // Get the current cell's text.
  var wb = SpreadsheetApp.getActive(), sheet = wb.getActiveSheet();
  var cell = sheet.getActiveCell(), value = cell.getValue();
  var len = value.toString().length;
  if(len == 0) return;

  // Change the color every 2 characters.
  var newCellData = Sheets.newCellData();
  newCellData.textFormatRuns = [];
  var step = 1 / len;
  for(var c = 0; c < len; c += 2) {
    var newFmt = Sheets.newTextFormatRun();
    newFmt.startIndex = c;
    newFmt.format = Sheets.newTextFormat();
    newFmt.format.foregroundColor = Sheets.newColor();
    newFmt.format.foregroundColor.green = (c + 2) * step;
    newCellData.textFormatRuns.push(newFmt);
  }

  // Create the request object.
  var batchUpdateRQ = Sheets.newBatchUpdateSpreadsheetRequest();
  batchUpdateRQ.requests = [];
  batchUpdateRQ.requests.push(
    {
       "updateCells": {
        "rows": [ { "values": newCellData } ],
        "fields": "textFormatRuns",
        "start": {
          "sheetId": sheet.getSheetId(),
          "rowIndex": cell.getRow() - 1,
          "columnIndex": cell.getColumn() - 1
        }
      }
    }
  );
  Sheets.Spreadsheets.batchUpdate(batchUpdateRQ, wb.getId());
}

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Edit: Depending on how the value of the cells to be formatted are set, including the value of the cell in the same request may be necessary as well. See this example on the issue tracker