Objects at "ordinary" temperatures (say, less than about 1000°F) are much too cold to emit a significant amount of visible
radiation (they emit infrared radiation, but that isn't detectable by the eye). However, if they are illuminated by some external light
source (e.g., the Sun, a flashlight, etc.), they may reflect a portion of that radiation and be seen by that reflected light. Which portions of
the illuminating radiation are reflected depend upon the chemical properties of the surface of the object. The surface may be prepared with
various dyes or paints to reflect some wavelengths more efficiently than others.
In the photo above, a flashlight sends "white" light onto a flat surface and that surface reflects the blue and red
portions of the light (and absorbs the green part) giving rise to a magenta color for the reflectesd light. The spectrum shows the presence
of blue and red but a dark region where the green is missing.
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