No they did not.
That rule was changed in August 2015, and the caucus was not held until March 1. Any voter could vote in the caucus as long as they registered Republican 30 days prior to the election.
Nobody was deprived of their right to vote. But apparently, a whole lot of people couldn't be bothered to put forth the effort to exercise it.
Everywhere else in the country, voter turnout has been at record numbers. How do you explain that this wonderful new system in Colorado resulted in a few thousand making the decision for over 1 million? Don’t blame it on Colorado voters—put the blame where it belongs, on a system designed to accomplish exactly the result it got: A few percent of the voters making the decision for all the others.