[Dan Lawrence]

I registered to post this! Here is a cached version of that page with the solution (thanks Google)… This had me scratching my head for about half an hour!

Thanks to MutantPixel for the solution:

“The eyedropper tool whether directly selected or temporarily selected via ‘ALT’ with the brush tool feeds what it samples into the ACTIVE color. You can set the Foreground color as active, or the Background as active. If someone were to accidentally click on the BG color swatch itself in the color palette, they would set that one as the active color. It all still remains foreground and background, however, if the BG is set as active, then all future eyedropper samples would update the BG color instead of the FG.

Give it a try, open the color palette, click the color that is the BG color, you’ll see the grey square around it is now black, it is now the active color (likewise the FG has a grey outline now) Whenever you sample with the eyedropper, it will sample to the BG color. Want to switch back to sampling the FG color. just click that little FG swatch and it will work the way you expect. It has been like this since ver. 2 of Photoshop, when I started using it.”