Josh, this sort of situation (a manager who believes that there is nothing really worth worrying about that would require money being spent to make it "look pretty") can come up in the corporate world fairly often. Many college students don't get exposed to this corporate culture (AKA "office politics") until after graduation, when you get your first "real" job. Some students already know what to do; others (usually the "nerds") can be bewildered until they learn.
As a summer job at a Taco Bell could be considered a "throw away" thing (you'll be quitting it by Labor Day anyway) you could use it as a learning experience of office politics. Part of that is picking your battles, what to let slide, what to worry about, how to tactfully address problems without causing embarrasment to a boss, and such. Something like a green wire misused as a voltage carrying conductor is not likely to be an immediate hazard to anyone other than another electrician, and an experienced electrician should be able to spot the violation easily enough. So I wouldn't argue it with the boss beyond one mention. But if thre's a 14 gauge wire only protected by a 150 amp breaker (that is a serious hazard) I'd mention it to the company district office. Tell them that you're an EE student, not a licensed electrician, but that you believe that there is a serious life and property threatening violation present, and could someone check it out before a fire happens?. Someone at the company district office who knows and is responsible for electric safety and liability should then come out and have a look. Maybe you misread the breaker ("That's only a 15 amp breaker") or such. That way you didn't cause the company a problem with city hall getting involved if it turns out to be nothing. You'd still lose a few "brownie points" with your boss, but not as many if city hall was involved. It's then their butt on the line if they miss a problem, not yours. And if a fire did happen, there would be smoke alarms and exit doors there so people should be able to escape it (The various safety building and electrical codes have redundancies built in so one mistake would be "caught" by other things being correct).
Companies, like people (and companies are in reality nothing more than groupings of people) don't want to have to spend money on something they believe isn't "broken". Especially in some operation that has a very low profit margin, like a fast food joint.