They are normal (classic) bootstrap classes. This is already in Tinymce (e107 version) and I missed them in forum. It's related to css and they are changed to div element, so they should be validated.
Rideblue2 use bootstrap, so those classes should be styled by default: https://getbootstrap.com/docs/3.3/components/#labels
Easy to change color in style.css file.
I really don't know why I used tag div not span... maybe to have possibility to use more html tags inside it??? No idea.
By the way - you can select only standard classes from dropdown, but you can rewrite it to any class your theme use - f.e. yellowlabel - it will use any class you sent as parameter (only dropdown is limited).