Try this test: Open up a new psd using the default photoshop settings (RGB colour/8 bit; Color Settings: North American General Purpose 2; proof setup - working cmyk) and fill the bg with any colour (for example #ff0000) now do a screenshot of anything, then open up the screenshot png in photoshop. Now switch between the psd and the png and watch the colour in your palette in your photoshop toolbar change!
Anyone know what's going on?! It's happened a few times to me, on different macs
I just captured a portion of the screen using 'CMD+SHIFT+4' and then opened the PNG file in Photoshop. The file had an embedded profile: my monitor profile.
Leopard (10.5.6)
I have set my computer to save screen shots as jpegs
Of course! It was even worse for a while when Apple saved screen shots as PDFs. You want as small a file as possible when you make a screen shot—unless you want it in a book that's going to be printed.
<http://www.pixentral.com/show.php?picture=1hjdSszuV8cyh9MvShsDRQ6iseuTF>
It can also be done through Cocktail and other utilities.