text: Title: module 'labelme.utils' has no attribute 'label_colormap'
  Body: ### Provide environment information
  
  I am trying to convert my .json files containing my labels (semantic segmentation, polygonal bounding box information) to VOC segmentation format for visualizing the segmentation masks over the input pixels of my image. I then get the error:
  
  module 'labelme.utils' has no attribute 'label_colormap'
  
  I am following the example here for VOC segmentation format dataset creation: 
  https://github.com/wkentaro/labelme/tree/main/examples/semantic_segmentation
  
  (base) pravin@AdminisatorsMBP SEGMENTATION % 
  
  ./labelme2voc.py Images_To_Segment Images_To_Segment_voc5 --labels labels.txt
  
  Creating dataset: Images_To_Segment_voc5
  class_names: ('_background_', 'vein')
  Saved class_names: Images_To_Segment_voc5/class_names.txt
  Traceback (most recent call last):
    File "/Users/pravin/Documents/SEGMENTATION/./labelme2voc.py", line 95, in <module>
      main()
    File "/Users/pravin/Documents/SEGMENTATION/./labelme2voc.py", line 56, in main
      colormap = labelme.utils.label_colormap(255)
  AttributeError: module 'labelme.utils' has no attribute 'label_colormap'
  (base) pravin@AdminisatorsMBP SEGMENTATION % pwd
  /Users/pravin/Documents/SEGMENTATION
  
  
  Please help. 
  
  I tried:
  
  cd labelme
  pip install -e .
  
  But this did not fix the issue. 
  
  
  ### What OS are you using?
  
  Mac OS Ventura 13.2.1
  
  ### Describe the Bug
  
  I am trying to convert my .json files containing my labels (semantic segmentation, polygonal bounding box information) to VOC segmentation format for visualizing the segmentation masks over the input pixels of my image. I then get the error:
  
  module 'labelme.utils' has no attribute 'label_colormap'
  
  I am following the example here for VOC segmentation format dataset creation: 
  https://github.com/wkentaro/labelme/tree/main/examples/semantic_segmentation
  
  (base) pravin@AdminisatorsMBP SEGMENTATION % 
  
  ./labelme2voc.py Images_To_Segment Images_To_Segment_voc5 --labels labels.txt
  
  Creating dataset: Images_To_Segment_voc5
  class_names: ('_background_', 'vein')
  Saved class_names: Images_To_Segment_voc5/class_names.txt
  Traceback (most recent call last):
    File "/Users/pravin/Documents/SEGMENTATION/./labelme2voc.py", line 95, in <module>
      main()
    File "/Users/pravin/Documents/SEGMENTATION/./labelme2voc.py", line 56, in main
      colormap = labelme.utils.label_colormap(255)
  AttributeError: module 'labelme.utils' has no attribute 'label_colormap'
  (base) pravin@AdminisatorsMBP SEGMENTATION % pwd
  /Users/pravin/Documents/SEGMENTATION
  
  
  Please help. 
  
  I tried:
  
  cd labelme
  pip install -e .
  
  But this did not fix the issue. 
  
  
  ### Expected Behavior
  
  _No response_
  
  ### To Reproduce
  
  _No response_