No because the State legislature has decided to allow legislative matters to be decided by popular vote. It's a Colorado State constitutional question, not a Federal question.
But there are federal laws which state the governing rules must be in place prior to the election. This was the basis for the Supreme Court ruling against Gore which went 9-0.
That's a debatable point; the CO state law permitting popular initiatives cannot supercede the U.S. Constitution. In any event, that's an issue of constitutional interpretation, and hence, for federal court.