This article references a “green brief.” What is a green brief?
It’s an indication that you’re seriously behind in your laundry.
The Supreme Court uses a color-code system for covers of briefs. They require that persons submitting briefs use the proper color cover for easy reference and identification. Amicus briefs, like those mentioned in your link, are required to bear either a light green cover if it’s in support of the plaintiff, petitioner, or appellant, or a dark green cover if it’s in support of the defendant, respondent, or appellee.
The complete Supreme Court rules, including all the various brief cover colors, can be read in this PDF.