Another restriction

For PCX or BMP files:

• With a color depth of 16, 24, or 32
• You MUST:
  • Set the video mode and create the onscreen window
  • Before you call load_bitmap to load the image file.

Otherwise, the colors may not be correct. 

This is confirmed by the documentation, which states:

"If the file contains a truecolor image, you must set the video mode or call set_color_conversion() before loading it."