Applying an adjustment to each layer seperately and simultaneously?

[Zirngibism]

How would one go about color correcting an entire image, layers and all?

See, I've got a massive layered file, with several layers I plan to paint on, but after calibrating my monitor it's all way too dark.

So I need to adjust the levels of the whole layered image-- meaning every layer simultaneously WITHOUT flattening the image, and also WITHOUT using adjustment layers (because you can't color-pick under an adjustment layer without messing up what you pick up-- I've tried it :( ).

It seems so simple- like something PS has got to have...

Thanks.

[Iridyse]

Hm, for some reason I thought selecting multiple layers and then doing a Image->Adjustment should work, but it doesn't.
One way of doing this would be to make an adjustment layer with the corrections and put another layer on top where you do the new changes, so you can still colorpick from the lower layers but you paint on the highest one. Not very efficient but...