Why do we see the color orange?
The human eye has two kinds of photo receptive cells, rods and cones. Rod cells are those that are not very sensitive to the color of light falling on them. They largely function as cells that detect the presence or absence of light and therefore pass on signals of black and white to the brain. The cone cells on the other hand are responsible for color and visual sharpness. There are three types of cone cells that are sensitive to either of green, red or blue light. These three colors can be used to create all other colors in our visible spectrum. The color orange is one which can be created by mixing red with a little bit of green.
If a body has an outer surface such that all of blue is absorbed, all of red is reflected and a small portion of green is also reflected, the reflected light from the object is perceived by our eyes as orange. It is the proportion of red, blue and green absorbed/reflected by an object that determines if it appears orange in color.