Color

FIG. 6-40 A white surface reflects all light that falls on it. A green surface reflects only green light and absorbs the rest. A black surface absorbs all light that falls on it.

Bundles of light rays are reflected diffusely in all directions from every point on an object. Only a few light rays are shown from only one point on a tree in this illustration. The lights that move to your eyes enable you to see a particular point from which they were reflected.

Interference and thin films

In a thin film, light can be reflected at the top of the film or from the bottom of the film.  Depending on the thickness of the film, the waves of light can show constructive or destructive interference.  If the phases of the waves are off by 180° then destructive interference will occur and that wavelength will be cancelled out. 

This removal of some frequencies or colors and the strengthening of other colors leads to the myriad of colors you see in the oil as it floats on water in a rainstorm.

For more on thin film interference, go to

http://physics.bu.edu/py106/notes/Thinfilm.html.