It being illegal at the federal level has nothing to do with whether an employer can test for it or not. Some employers test for tobacco & alcohol usage.
Actually, it is what employers are using when they are choosing to drug test and reject applicants - federal law. The universities are using that also. So, while, CO has legalized using marijuana, employers are able to still “discriminate” and “drug test” because of overriding federal law.
Preventing the discrimination suits, so far. They are bound to come, though.
And yes, an employer can have performance expectations. I have not heard of employers not hiring/firing someone for tobacco use in CO, but I know they are pushing things like not having smoking areas on work property, offering smoking cessation programs free of charge.