|MadSci Network: Microbiology|
I can't tell you exactly what was on your bread samples without testing them, but I can make a good guess. You probably have the same types of common bread molds on all your treatments. What might have happened with the low-moisture/dark treatment is that this mold had a harder time growing and did not get to the point of producing spores or pigments that it might have produced under the other conditions. Some molds require a bit of light to induce sporulation. Many common molds will appear white when only the initial mycelia are growing. Often, pigments are not produced until the spores are being formed. That would be my guess. To test this theory you could look for spores from your moldy bread under a microscope. If you can't find any with your "white" mold sample then this theory makes some sense. You could also put a piece of each type of mold from your treatments on a growth medium such as potato dextrose agar in a petri dish and let them grow to see if they look the same under the same growth conditions. Hope that helps.
Reference: Developmental and photoregulation of three Neurospora crassa carotenogenic genes during conidiation induced by desiccation. Fungal Genet Biol 1996 Feb;21(1):101-8
Try the links in the MadSci Library for more information on Microbiology.