Without a picture, it's hard to see what you have. But As Arthur Dent would say, "Don't panic." More than likely, it's a cosmetic mould.

A slight discoloration could simply be mildew. You have a darkened area, with water under the decking, over a basement with probably standing water? I wouldn't be suprised. You find that on framing lumber from simple humidity when it's banded and covered. And it's not an OSB issue. Can you post a picture?

Whether you have mold, mildew, or fungus is irrelevant.

It can be cleaned with solutions of bleach, soap and water with no lasting effects...health or otherwise.

I will try to get a picture posted. But I can tell you that you have already given me hope for a better night's sleep. Thanks for the feedback and info.

Do let us know what the inspector says.

Molds and mildews *can* become a serious problem in homebuilding, especially when the wood is exposed to the elements during extended periods of wet. Yes, one can find some types of molds already present on lumber from the lumberyard, and yes, those molds often are not problematic. However, there are just enough cases where the residents suffer severe allergic reactions (to buildings which were later determined to have molds and/or mildews) that one should apply more than casual care in diagnosing and cleaning the affected areas. The problem is not necessarily caused by those cosmetic molds, but occurs when the raw wood is damp/wet for an extended time, which then forms the perfect environment to allow other types of airborne spores to infest the bare wood. Katrina aside, IMO, the more humid your climate and the farther south your geographical location, the more one should be concerned.

Let's see if this works. I tried to take various views of the underside of the floorboards. There is only one board that doesn't have black spots.

Here is a link that might be useful: Mold???

Er...no offense....but when I first looked at them; I was wondering what you were referring to. No, that is NOT a defect of the OSB. It's simple mildew (from what I can tell from looking at the pictures, not being on-site, and lacking a full, pressure-suited and complete laboratory analysis of the black spots).

I do see some other issues, though.....

Please share...what other issues?

Contrary to popular lore, chlorine bleach is not very effective against stachybotrys spores that cause toxic black mold on damp cellulose rich materials.

Don't forget that spores move easily through the air when disturbed so disinfecting is sometimes not as important as lightly spraying and then washing all surfaces and thoroughly drying the area so it won't become reinfected.

Always wear an N-95 or N-100 respirator as well as skin and eye protection. Keep a lot of air moving through the work area and never mix bleach with other cleaning products because gases can be produced from contact with acids and/or ammonia that can cause immediate and irreparable damage to your lungs. Chlorine gas was a favorite of the Germans in WWI.

If the mold is determined to be toxic black mold hire a professional.

I'm not sure about the cost, but there are many mold abatement and pre-treatment options available. With just the framing up, it might be very cost effective to have everything pre-treated. That would probably give you peace of mind and a warranty against any mold.

Stachybotrys is found VERY infrequently. If you're concerned, certainly get it tested; but from the pictures, what is shown there is very common.

Anyhow, the other concerns I had were the long runs of those electrical wires....seems beyond code, looking at the pictures. Second, I notice a number of spots where they've smeared off the construction adhesive; prime spots for floor squeaks. I'd walk the entire floor once dried in and replace any nail areas with screws that might squeak. And...well...never mind. Too late for the jack post.

Seriously; it looks fine and I wouldn't worry about it.

Unless your electrician isn't finished down there, the wiring runs aren't tagged to the joisting, in one picture only supported by a 16d nail. It could be everything is just running wild for now and he/she will fasten them up later? That ducting return seems to be hanging out there in space unsupported as well.

I'm really appreciating everyone taking the time to respond and comment. We are actually having this home built through our building trade's program at our high school. The wiring and HVAC will be completed by the licensed company we've contracted with. Since we are at the mercy of not only the weather but also available hours in a school day, the tasks are completed somewhat sporadically. It can try the patience but the students are really getting some invaluable experience.
Thanks for the tip on the extra screwing Jasonmi7. I have noticed a small bit amount of squeaking in some areas and that would explain it.
Thanks again.

Too late for the jack post.

Good eye! It looks like at least two of the posts are sitting on top of the floor, rather than buried in the concrete as they should be. They must be secured to the floor--and hopefully there is an underlying pier-- with appropriate length expansion bolts. On one home I built, the engineer insisted that all four posts be bolted to the underlying piers before the concrete slab was poured. As well, the attachment to the beams doesn't look complete either.

the attachment to the beams doesn't look complete either.

Took another look. It definitely isn't complete. There is no lateral support and probably not enough bearing support either.

Check your plans. The attachment should be spelled out.