One of the major changes in the new material settings for FDM is the way colors are added to materials. Formerly we would treat every color of filament as a material, now it has become a property of that material, which reflects the practice of selling different colors of the same filament for the same price.
Colors are now added in the "execution" part of the material, just like layer thickness or filling density. To add a color you can
select one from the list available:
As you can see the selected color appears below the selection field.
Or you can simply start writing the name of your own color, let's say terracotta:
Once you've finished writing you click "Add terracotta"
and the new color is added:
This is what it will look like on the widget: