Things may get interesting for Colorado casinos. The state’s only horse racing track isn’t the only group proposing ballot measures for voters to consider this fall. Last month, the owners of Arapaho Park horse racing track in Aurora filed six proposed ballot measures calling on Colorado voters to allow it to have up to 2.500 slot machines or video lottery terminals at its horse racing track in Arapaho County or where it offers parimutuel betting of those races in Mesa and Pueblo counties. To counter that, the casino industry has proposed a few measures of its own, all of which…