If the gifts are deductible, the actual cost of the donation is reduced by your tax savings. For example, if you are in the 33% tax bracket, the actual cost of a $100 donation is only $67 ($100 less the $33 tax savings). As your income tax bracket increases, the real cost of your charitable gift decreases, making contributions more attractive for those in higher brackets.
Small particles of dust and pollution in the air can contribute to (and sometimes even enhance) these colors, but the primary cause of a blue sky and orange/red sunsets or sunrises is scattering by the gas molecules that make up our atmosphere.
Color saturation determines how certain hue will look in certain lighting conditions. For example, a wall painted with a solid color will look different during the day than it does at night. Because of the light, the saturation of the wall will change over the course of day, although it is still the same color. When the saturation is zero, what you will see is a shade of gray.