DataValidation.gs

function initDataValidationCells() {
 
  var SHEET_NAME = "September 2019";
 
  var sheet1 = SpreadsheetApp.getActiveSpreadsheet().getSheetByName(SHEET_NAME);
  var dataRange = sheet1.getDataRange();
 
  var PINK = "#ff00ff";
  var GREEN = "#00ff00";
  var LIGHT_BEIGE = "#fff2cc";
  var YELLOW = "#ffff00";
  var BLUE = "#cfe2f3";
  var ORANGE = "#ff9900"; //group or corporate
  var GOLD = "#f1c232"; // extra slot for inconsistent availability or special needs
 
  for (var i = 1; i <= dataRange.getNumRows() ; i++) {
    for (var j = 1; j <= dataRange.getNumColumns(); j++) {
     var bg = dataRange.getCell(i,j).getBackground();

      if(bg == PINK ||
         bg == GREEN ||
         bg == LIGHT_BEIGE ||
         bg == ORANGE ||
         bg == YELLOW ||
         bg == GOLD ||
         bg == BLUE)            
             {
         
             var cell = dataRange.getCell(i,j);
             var range = SpreadsheetApp.getActive().getRange('Volunteers!A2:A');
             var rule = SpreadsheetApp.newDataValidation().requireValueInRange(range).build();
             cell.setDataValidation(rule);
           }
    }
  }
 
}