CA Veh Code Section 27603

When a motor vehicle formerly used as a schoolbus is sold to any person and is used exclusively for purposes other than the transportation of pupils pursuant to Article 3 (commencing with Section 39830) of Chapter 5 of Part 23 of the Education Code, it shall be painted by the purchaser a color different than that prescribed by the Department of the California Highway Patrol for schoolbuses before it is operated on any street or highway other than to have the vehicle painted or moved to a place of storage.

The provisions of this section shall not apply where the ownership of a schoolbus is transferred to a nonprofit organization under a contractual arrangement under which the ownership is required to be retransferred to the original owner within 90 days of the date of the original transfer.