When I try to toggle between current settings and defaults, I get a blue or black screen in the "After" image so I can not compare before and after. The toggle doesn't work when I am viewing a single image or when I am viewing before and after side-by-side. The blue or black image looks like the image is totally clipped, but it's the same whether clipping is on or off. Command-Option-P does not work either. Also, the histogram totally disappears when I try to toggle. So I think something is corrupted, and I'd like to know how to fix it. BTW, this toggle works fine when I am in the adjustment brush panel; it's the basic panel where it doesn't work. I use Photoshop CC (2014) and Bridge CC on a new iMac--Yosemite. All are up to date (ACR 126.96.36.1991). I am not using Lightroom. I would appreciate a suggested fix. Confession: I am very new to the Mac environment and just returning to Photoshop after an absence so I'm finding my way; there's a good chance I'm making a rookie mistake. Thanks in advance for any help or suggestions on where else I might post my question.