I'm running Photoshop CS3 Extended in 32 bit Vista. Whenever I need a layer filled with 50% Gray I have been accustomed to select it from the default swatches palette (last box on the right side of the first row). However, I have just discovered - perhaps belatedly - that the RGB values that this selection produces are NOT R 128, G 128, B 128 but can vary between 131 and 147 depending on the color profile of the document that I am using at the moment.

I can verify that it is not 50% Gray by then changing the blending mode of the new layer to Overlay which, at least in theory as I understand it, should produce no color change to the underlying layer. However, I do observe changes.

I have also confirmed with others that this behaviour is the same for CS3 running in XP on a different make of computer.

Am I missing something fundamental?