code: def _get_fillcolor(resource_type, properties, known_sg=[], open_sg=[]):
      
      fillcolor = None
      # check security groups
      if 'SecurityGroups' in properties:
          # check for external security groups
          for sg in properties['SecurityGroups']:
              if 'Ref' in sg and (sg['Ref'] not in known_sg):
                  fillcolor = 'yellow'
                  break
  
          # check for open security groups
          for osg in open_sg:
              if {'Ref': osg} in properties['SecurityGroups']:
                  fillcolor = 'red'
                  break
  
      # LoadBalancer
      if resource_type == 'LoadBalancer':
          if ('Scheme' not in properties) or \
                          properties['Scheme'] == 'internet-facing':
              fillcolor = 'red'
  
      return fillcolor
docs: Determine fillcolor for resources (public ones in this case)