I've had washing acquire "the damp smell" when I left it wet for too long after taking it out of the machine. At least, I think that's what caused it. It might be possible that, when you do your whites, you are in a bit more of a hurry and therefore dry them straight from the machine, avoiding the damp smell. (E.g. bed sheets washed, dried and back on the beds in a few hours.) Make sure your coloured clothes aren't sitting around in the machine or in a basket before you hang them out. Hope this helps.