This morning's news reveals that Colorado governor Owens vetoed the bill to add gender identity and sexual orientation to the state's workplace anti-discrimination code.
In his May 26 veto letter , Owens said that a 1990 law called the "off-duty conduct statute" already protects gay employees from being fired for their behavior outside the workplace, and that the bill "had the potential to be costly for Colorado businesses due to an expansion of their tort liability."
This logic would not seem to extend to employees transitioning from one gender to another in the workplace, but Owens made no comment on that issue.
In addition, I looked to find the case that the Governor referred to when he said "The Colorado courts have ruled that homosexual employees who claim to have been fired because of their off duty sexual conduct already have the right to sue their employers for money damages under this statute." The only Colorado case on Lexis involving a gay plaintiff and the off-duty conduct statute, section 24-34-402.5, (also called the "lawful activities" statute) is Ozer v. Borquez, 940 P.2d 371 (Colo. 1997). In it, a gay lawyer sued for discharge based on his sexual orientation. The Supreme Court of Colorado's opinion stated that the trial judge did not utilize the off-duty conduct statute, relying instead on the Denver sexual orientation anti-discrimination ordinance. And in footnote 6, the Court specifically stated as follows: "We do not decide here whether Borquez was entitled to have his claim of wrongful discharge submitted to the jury based on the lawful activities statute."
Unless Lexis is lying, I don't think there is any such published case in Colorado.