The Colorado Senate is headed for a showdown over same-sex unions. A Democratic senator has proposed a bill to smooth Colorado’s transition from civil unions to same-sex marriage equality. The measure would answer questions like: Do couples currently in a civil union now need to marry? The measure seems pretty mundane, but the GOP-controlled Senate is expected to reject it. That’s because the nation’s highest court hasn’t ruled on same-sex unions, leaving opponents to gay marriage hoping that a lower federal ruling granting Colorado couples marriage rights will be overturned. A Republican committee takes up the bill tomorrow.