|MadSci Network: Microbiology|
It is possible for fungi to be different colors, but what is most likely the explanation is that you saw different types of fungi. THE "bread mold" is Rhizopus, a blackish fuzzy fungus, but it is not the only one which grows on bread. Another common one on bread is Penicillium (the one which can produce penicillin) which is a bluish-grayish-greenish fuzzy fungus usually with a whith border. When my fourth-grade son did a science project on mold growth on bread, the one which he found was Penicillium.
Fungi are a diverse and interesting group of organisms from which we get medicines (penicillin as mentioned before) and foods (mushrooms are the fruiting bodies of certain fungi). They are also used in production of cheeses, breads, wine, and beer. Of course, we hardly care about all that when we want to make a sandwich and there's a black fuzzy mess on the bread!
To learn more interesting things about fungi go to http://www.herb.lsa.umich.edu/kidpage/factindx.htm
Try the links in the MadSci Library for more information on Microbiology.