What are the different hard hat color codes?

■ White

• for engineers, managers, supervisors, and foremen
  

  ■ Blue

• for electricians, carpenters, and other technical operators
  

  ■ Yellow

• laborers
  

  ■ Green

• safety officers
  

  ■ Brown

• workers with high heat application
  

  ■ Gray

• site visitors

Why is there a need for hard hat color codes?

Aside from easily classifying the job of someone, in a way, it's usually because of what is desired in the construction process -- speed/productivity. The thing is, when everything's sorted out quickly, you'll easily be able to request the necessary manpower to conduct such action; say, you'll be needing laborers to pull out some materials, you can easily call them out, and same goes with the other workers - the manager will be able to delegate tasks efficiently if he/she knows the proper group he can assign those tasks to.

What's my takeaway from the site visit?

The thing that was usually taught concerning hard hat color codes didn't really reflect what was on-site. For example, the ones wearing blue were steelman, orange were concerned with the building utilities, and green were the masons -
as shown in the photo above._{Though I'm sure it was more of a uniform thing than of what was the standard "color".}

Source:
¹Hard hat color codes