Why are some chickens yellow skinned and some white?

A chicken's skin color comes from the diet it was fed and the same bird
could have a white skin or a yellow skin, depending on what it ate. The diet
that produces a yellow skin is more expensive than the usual diet, but the
people at Perdue Farms feel it's worth it because a yellow skin color is one
of the fastest ways Frank's inspectors have of finding and disqualifying an
inferior bird.

If a bird is sick or off its feed, it doesn't absorb
nutrients well and won't develop the rich golden color that is
characteristic of Perdue birds. Also, if part of a bird's outer skin is
"barked", that is, rubbed off due to rough handling during processing, the
Perdue inspectors can detect it more easily than with a white-skinned bird.
Detecting and removing and chicken with a barked skin is important because
damaged skin shortens the shelf life and dries out and toughens the meat.

No white colored chickens get by the inspectors.

Sometimes when I open a package of chicken, there's a pungent odor that
doesn't smell spoiled, but it's definitely unpleasant. Should I throw the
chicken out?

If the odor lasts only a matter of seconds, your chicken is probably fine.
Meat is chemically active, and as it ages, it releases sulfur. When you open
a bag that doesn't have air holes, you may notice the accumulated sulfur,
but it will quickly disperse into the air. In fact, I've heard of cases
where a wife will lean over to her husband and say, "Smell this, I think
it's gone bad." He'll take a deep whiff and find nothing wrong with it.

She'll take another sniff and then wonder if it was her imagination. It
wasn't. It's just that once the package was opened, the sulfur smell faded
into the air like smoke rings.
If the chicken still smells bad after a couple of minutes, that's an
entirely different story.

The problem is bacterial spoilage or rancidity or
both. Return the chicken to the store where you bought it and write to
Frank. If a chicken's been around too long you can smell it, and if you
can't detect it at room temperature, you probably can as it cooks, since
rancidity is more obvious at higher temperatures.

Rancidity can occur without bacteria if the freezer where the meat was stored wasn't cold enough
or if the product was kept there for a very long time, such as more than six
months for uncooked chicken, or more than three months for cooked chicken.
(By the way, I don't like to focus on this unpleasant stuff, but I do want
you to get your money's worth when you're buying chicken.)