This reminds me of a similar question I used to use in my classes
"What size ground for a 200 Ampere service"

Which can't be answered with the information given.
The definition of ground is "Ground. The earth."

I think I know what the OP is asking about ("what color is it and what does it do"- Mike Holt)

To the OP, if you would ask using code terms then its a simple process to answer your question.
Grounding does not have to be confusing, "we have met the enemy and he is us" Pogo