Global Attributes can be added going to Products > Attributes.
Each Global Attribute has terms, for instance, a Color Global Attribute can have “black” or “green” terms. To add terms to a Global Attribute, just click on the button on the right.
The term table will show additional columns for Color and Text, options you can configure for each term.
Now while adding a new term, or editing an existing one, you will have the option to setup a color, custom text and type of display