You can use a photodiode to detect the intensity of light falling on its sensor, but it does not respond to individual cycles of the light (it does not work at the frequency of light, and neither will any circuit connected to it. A 555 timer, for example, cannot operate at the frequency of light.
As already proposed, optical filters over 2 or more sensors can be used to distinguish the colour content of the light. Have a look at some basic colour camera designs.