If you use Photoshop to create or edit an image then it will contain embedded information about the ‘Color Mode‘. To set up a dropdown attribute that displays and allows you to search for the ‘Color Mode‘, follow these steps:

• Create a new attribute of type ‘dropdown‘ called ‘Color Mode‘. Click ‘Show on search‘ if you want to show the dropdown on the ‘advanced search‘ page.
• Add attribute values with the following names and IPTC/EXIF Mapping fields:
  
  
  • Bitmap: 0
  • Greyscale: 1
  • Duotone: 8
  • RGB Color: 3
  • CMYK Color: 4
• Create an ‘embedded data mapping‘ to map the embedded field XMP:Color Mode to your attribute.