It's the color labels set to items in database.
The concept is the same than Tags, but with a specific signification defined by user.
The list of image with same color labels can be show in Label tree-view from left sidebar.
This concept exist also in LR and values are also recorded in image metadata if right Setup/Metadata options are turn on.
Note Pick labels (Flags) are also available, as under LR. There are used in photo workflow to identify the image to review, to select, to delete, or to archive (for ex).
Gilles Caulier