Seems like the "Equal Pay for Equal Work Act" which you're referring to only applies to US companies. And if it doesn't, how does Colorado ever plan to enforce, say, a company out of Estonia, to follow this law?
Companies outside the US which employ US residents are subject to US labor laws (if they never employ any US resident, then of course it is not relevant).
The question you are asking is substantially equivalent to asking why an Estonian company must pay US payroll taxes and how such laws could be enforced.
The question you are asking is substantially equivalent to asking why an Estonian company must pay US payroll taxes and how such laws could be enforced.