Your lips are red because there are many blood vessels around the lip area and because the skin on your top and bottom lip is very thin the color from these blood vessels is seen through to the surface of the lips, making them appear red. This also explains the reason why your lips turn blue in cold weather. The cold air makes the blood vessels in your skin tighten and contract, forcing the blood to go deeper into your body to hold in the warmth. This makes your skin look paler and your lips look blue, it's been known as sign that you need to be warmed up for thousands of years. This is one possible explantion for why we find lips so attractive, we think of red lucious lips as a sign of warmth, good health and invitation. This redness of the lips has been artificially created through lipstick since Mesopotamian times, over 5000 years ago.

As the "white" light of the sun rays enter the Earth's atmosphere, blue light is scattered by molecules in the air. Usually, light travels in a straight line of course however if it hits something (i.e. molecules, dust, pollution, water) that causes it to bounce off, deflect, refract or scatter in different directions. The size of particle determines how the light is scattered. Small particles scatter the shorter wavelengths, such as the blue and violet/ ultraviolet wavelengths, larger particles however scatter the longer ones, like red. Eventually particles become large enough to reflect all wavelengths and the light appears white.

Air molecules are just the right size to scatter the shorter wavelengths of blue to violet. The blue scattering begins at around 18 miles up. The blue light waves are scattered all over the sky in all directions. So, no matter which direction you look, blue light appears. On hazy days, moisture droplets (or numbers of water particles larger in size than air molecules) reflect all wavelengths equally making the sky appear either white or grey. All colours seen in the sky are the result of scattering caused by molecules or particles in the atmosphere and so polloution can cause the sky to sometimes look brown or yellow.

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