How can I tell if my dog is going blind?

I know that blindness is usually marked by a cloudy eye, but I have a 7 month old Australian Shephard/Blue Heeler mix (her name's Penny). I adpoted her and at the agency they told me that her eyes would change from blue to brown. They weren't completely blue. Two months later, her right eye turned completely brown, and her left eye stayed half/half. Is this just a defect, or is she going blind? We're taking her to the vet anyway, but they're closed for the weekend and I'm worried. There's no cloudiness, just blue. Nothing's wrong with her pupils, either, it's all around her iris.