I think that's an excellent question, and one I can't answer with any specifics. I'm no expert in CO election law, but I would be surprised if the backers of this initiative haven't had CO attorneys who are expert check the form of the referendum question.
I tend to assume that the referendum backers had at least some legal opinions to support their effort. Of course, one legal opinion is not the final word, and other experts in CO law may well have other interpretations. If a passed referendum changes the national result, I strongly suspect that there would be legal challenges to the application of the referendum in the current election.
Clearly they have received legal advice as to the specifics of how to go about doing something that really shouldn't be attempted to do in the first place. I assume a lawyer would advise the best way to get around particular problems, without ensuring that it will hold up to scrutiny.
First, the US Constitution grants to the legislatures the authority to determine the manner by which electors are appointed. But the Colorado Constitution asserts that legislative authority is reserved to the People, who have granted non-exclusive legislative authority to the General Assembly. Proposition 36 repeats that they are acting as the legislative authority. It also specifically provides that the General Assembly can change the manner by which electors are appointed. This appears to be intended to head off a federal case that the legislature had not instituted the change in the manner by which electors are appointed, and that somehow the Colorado Constitution is being changed to asurp the authority of a future legislature.
Even if the referendum passes and has no effect on the national result, it will be challenged in Congress when the electoral votes are cast.
It also has sections that purport to govern how the amendment itself would be put into effect, that would override the ordinary procedures for handling amendments to the Constitution. One would provide for an accelerated recount on the initiative itself if it were close. Another provides for an accelerated proclaimation by the governor so that it can come into effect in time for the electors to vote.
And finally it includes a severability clause so that the proponents can argue that ti doesn't really matter if the courts rule that it can't apply to the 2004 election.