when they are exposed to oxygen the apples become a brownish color and become softer and dryer than before. if you want your apples unspoiled for a period of time, get one of those green bags and...
Apples can be green, or red, or a yellowish color. If you like sweet and juicy stuff, eat a red apple, if you like sour stuff, eat a green apple, i dont know what yellow apples taste like.