It has been mentioned before in this thread. Oxidation, especially in its early stages, lends a metallic flavour to beer! Unless you take active measures to avoid it, it is highly likely that your home brew will suffer from oxidation issues and pick up this specific metallic flavor, that in effect dulls your beer. For example, if when your beer reached fg, and you move it to a secondary fermenting vessel with a significant head-space, it will quickly pick up the oxygen and develop the metal flavor. There's a link between what we refer to as metallic flavor and oxygen. Everybody knows with first hand experience that oxygen has a significant chemical impact on (untreated) metals. This chemical reaction can be observed as it results in stains and rust over time, but is also instrumental to what causes the metal to emit what we think of as metallic flavor or aroma. In fact, it is only untreated metal that emits this particular smell, and I especially notice it when I rinse and brush my cast-iron frying pan under running, hot water, or when I polish stained brass or copper. If you play the trumpet, you're an oxygen flavor connoisseur! In contrast, stainless steel cutlery does not emit that smell at all, because there's no oxygen reaction. Unlike untreated metals, beer doesn't rust or stain (hmmm, well, perhaps it actually does), but it is influenced by the same flavor impact. Over time, the oxygen flavor will change, and it will also start influencing your beer color - perhaps by similar reactions to those causing metals to stain and rust?