https://www.pbainbridge.co.uk/2018/12/check-cell-colour-and-loop.html

Check cell colour and loop.gs

function getAssigneeDetails() {
  
  // get 'Plan' sheet
  var planSheet = SpreadsheetApp.getActiveSpreadsheet().getSheetByName('Plan');
  // get 'Plan' sheet data range
  var planDataRange = planSheet.getDataRange();
  // get 'Plan' sheet data values
  var planData = planDataRange.getValues();
  // get number of last row of data in 'Plan' sheet
  var planLastRow = planSheet.getLastRow();
  
  
  // loop through each Assignee from 'Plan' sheet to get relevant details (skipping row headers) *********
  for (i=1; i<planLastRow; i++) {
    
    /* check Assignee cell is not blank before proceeding
    i = row, 6 = column - as is 2-D array */
    if (planData[i][6]) {
      Logger.log('Assignee cell is not blank');
      
      // get current cell of 'Assignee' column row. Add 1 to row value 'i' otherwise is a row behind
      var getCell = planDataRange.getCell([i+1], [7]);
      
      // get cell background colour of 'Assignee' column row. 
      var getCellColour = getCell.getBackground();
      
      // check Assignee cell colour is white
      if (getCellColour == '#ffffff') {
        Logger.log('Cell is white, will proceed');
        
        // get corresponding 'Room number' for Assignee
        var roomNumber = (planData[i][4]);
        Logger.log(roomNumber);
        
      } // end of 'if' for checking Assignee cell is white
      else {Logger.log('Cell is not white, will not proceed')};
      
    } // end of 'if' for checking Assignee cell not blank
    else {Logger.log('Assignee cell is blank')};
    
  } // end of 'i' loop through each Assignee ************************************************************
  
  
}// end of function


function onOpen() {
  SpreadsheetApp.getUi()
  .createMenu('Menu')
  .addItem('Email Assignees', 'getAssigneeDetails') // label for menu item, name of function to run.
  .addToUi();
}