The United States Supreme Court held that when a color meets the ordinary requirements of a trademark, there is no special rule preventing color alone from serving as a trademark.
Qualitex Co. v. Jacobson Products Co., 115 S. Ct. 1300 (1995).
Richard W. James,
Trademark Law - Lanham Trademark Act of 1946 - Trademark Registration,
Duq. L. Rev.
Available at: https://dsc.duq.edu/dlr/vol34/iss2/10