Section 21452 Of Article 3. Offenses Relating To Traffic Devices From California Vehicle Code >> Division 11. >> Chapter 2. >> Article 3.

. (a) A driver facing a steady circular yellow or yellow arrow signal is, by that signal, warned that the related green movement is ending or that a red indication will be shown immediately thereafter.
  (b) A pedestrian facing a steady circular yellow or a yellow arrow signal, unless otherwise directed by a pedestrian control signal as provided in Section 21456, is, by that signal, warned that there is insufficient time to cross the roadway and shall not enter the roadway.