An RGB color wheel which denotes complimentary colors. When Red wavelengths are absorbed, green light is observed, for example.
<a href="//commons.wikimedia.org/wiki/User:Danil_Satria" title="User:Danil Satria">Danil Satria</a>
<a href="//commons.wikimedia.org/wiki/File:Colorwheel.jpg" title="File:Colorwheel.jpg">File:Colorwheel.jpg</a>