function sumColoredCells(sumRange) {
  var activeRange = SpreadsheetApp.getActiveRange();
  var activeSheet = activeRange.getSheet();
  var formula = activeRange.getFormula();

  var rangeA1Notation = formula.match(/\((.*)\)/).pop();
  var range = activeSheet.getRange(rangeA1Notation);
  var bg = range.getBackgrounds();
  var values = range.getValues();

  var sum = 0;
  for(var i=0;i<bg.length;i++)
    for(var j=0;j<bg[0].length;j++)
      if(bg[i][j] == activeRange.getBackground())
        sum += parseFloat(values[i][j]);

  return sum;
};