[Photoshop] Transparent background is black?

Ive encountered problem recently and its ruining all my work in photoshop.
Problem is that when I set some parts of image transparent, background isnt
chessboard of white/gray squares, but its completly black (and I dont have any black
layer under it :P).
Any idea why?
Update: New>Bgcolor doesnt help :(

One thing Ive noticed is that when I select one of the RGB chanels, its normal transparent, but when I have selected whole RGB, its black. Another thing is that when I export the image, transparency is ok.
So anything thats wrong, is actual color of transparency.
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