What section of the code say that all conduit must be painted?

The National Electrical Code (NEC) does not explicitly state that all conduit must be painted. However, NEC Article 300.7 discusses the need for proper protection against corrosion for conduit exposed to harsh environments, which may imply that painting is necessary in some cases. Additionally, local codes or regulations may have specific requirements regarding the painting of conduit for aesthetic or protective reasons. Always consult local amendments and codes for precise requirements.