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"If we confine ourselves to the visible portion of the electromagnetic spectrum, and ignore the brain’s role in color perception (see: recent blue/black vs gold/white dress controversy) an object looks a certain color because: •It absorbs some wavelengths of light more than others (e.g. something looks red because it absorbs all the other colors). •It reflects certain wavelengths of light more than others (e.g. something looks red because it reflects red most readily into our eyes.)(or, if we want to explain photonic phenomena which give opal and butterfly wings their color, we need to specify that it reflects certain wavelengths in a specific direction)."

•A neon lamp appears to be a specific shade of orange because of transitions between energy levels in neon atoms which fall in the red-orange-yellow region of the spectrum. This is an example of emission causing a specific color, and it is the simplest case to analyze because it only involves unbonded atoms.

So to summarize, the colors of objects ultimately come from their elemental composition. But many different elements can produce the same visible color because 1) the visible part of the spectrum is a small portion of their color and 2) the specific way that an element bonds with others makes a difference. See also: How Animals Hacked The Rainbow And Got Stumped On Blue