$bgcolor = ($bgcolor == $oddColor ? $evenColor : $oddColor);
This is using the tenary operator, basically if the first element is true ($bgColor is the same value as $oddColor, then assign $bgColor to equal $evenColor. If it is false, then use $oddColor. On the next runthrough of this check, the opposite will happen. Like I said, though, both will work, this is just a way to keep it on one line.