Start a petition? I thought that was what I-140 is all about, unless I am misunderstanding you?
The Presidential Primary Election Initiative (I-140) Initiative 140 would restore presidential primary elections held before the end of March and make them open in Colorado. Currently, Colorado utilizes a closed primary system, in which only registered party members may participate in a party's primary. However, unaffiliated voters may choose to affiliate with a party on Election Day in order to vote in that party's primary.