Picked colours automatically are background colours, but I want them to be foreground colours, why??

Sorry for maybe not being clear enough, because my English isn't that good, but here's my problem:

Yesterday I was working in Photoshop and all of the sudden when I picked a colour (through the dropper or in the swatches panel, didn't make a difference), instead of the picked colour automaticcaly being the foreground colour (don't know if that's the correct word), it transferred as the background colour.

Of course I could just switch them, but when I pick a new colour, the same problem occured. So every time I want to paint in a certain colour I have to switch the background/foreground colour.  I don't understand what I did or what I should do to solve this. Because I just want to have a picked colour immediately be the foreground colour.