Tim, look a bit more closely at the picture.

In the white area, you can see that the white is in fact 3 dimensional. There are sections where it stands off in balls, like white mold will, and then a thin fuzz is spread out otherwise. The pattern of the balls and ridges is that of mold.

Also look closely at the darkened area. I thought too it was just blue stain, but looking closer at it it seems to be mildew instead. I say that for 2 reasons. 1: the color: it seems to be a deep brown-black, with little blue in it (take that for what it's worth, I know that color is affected by the picture and by my monitor's settings) 2: There are 'spots', many black circles, in the affected area, which is how mildew colonizes.

If you look elsewhere on the timber, there is certainly blue stain in this timber. So I could be wrong here. But to me it looks more like mildew...

If it were a condensations issue, not a water flow issue, I would expect to see the drywall in good shape. The water will collect on the coldest things present, which is going to be the wood, and it may not even be collecting in high enough quantities to be detectable to the casual observer, just enough to keep the wood damp would cause what I am describing, yet have no effect on the drywall.

To be clear though, I am not asserting that this must be the case here, I am just saying it is possible, and telling why. Like I said earlier there is no way I or anyone else can ever come up with an accurate scenario based on a picture, we would have to be able to see it to know for sure. All we can do is give you the information you need to be able to figure it out.

DLB