47 CFR 17.21: Painting and lighting, when required.

Antenna structures shall be painted and lighted when:

(a) Their height exceeds any obstruction standard requiring notification to the FAA (see § 17.4(a) and § 17.7).

(b) The Commission may modify the above requirement for painting and/or lighting of antenna structures, when it is shown by the applicant that the absence of such marking would not impair the safety of air navigation, or that a lesser marking requirement would insure the safety thereof.

(c) An antenna installation is of such a nature that its painting and lighting specifications in accordance with the FAA airspace recommendation are confusing, or endanger rather than assist airmen, or are otherwise inadequate. In these cases, the Commission will specify the type of painting and lighting or other marking to be used for the particular structure.