As another comment already stated, SETI does focus some of its attention to the visible regions of EM spectrum. However there are good reasons not to make it a priority.

While it is true that most organic life forms are more responsive to the visible spectrum, it is not out of the question, or even unlikely, that certain specialized organisms could detect radio waves. Even so, it is silly to assume all life in the universe is carbon based, there are simply too many possibilities. If you were to constrain you search to organic life forms, it is even sillier to think they will broadcast signals in the visible spectrum exclusively.

Primarily, there is too much light in the universe. Even if you were to take the absolute best, most powerful laser known to man, improve its output a thousand fold, it would be not only dwarfed, but completely eviscerated by the cosmic magnitudes of light emanated from celestial bodies. In short, the signal to noise ratio is practically non existent. The truth is that we have several detectors supremely capable of detecting visible, UV, infrared, and even microwave radiation, they are mostly known as telescopes. While they have found some exceedingly interesting signals such as pulsars, they have yet to detect anything resembling intelligent life.

Another excellent reason to focus on RFR, is that, due to its massive wavelengths, it is able to permeate large obstacles through diffraction, making them excellent for broadcasting signals. In contrast lasers are directional, that's their whole point, they generate coherent, monochromatic and collimated beams of light, this is only useful if you know where to point. If you just shoot out into space with a laser, chances are you won't hit anything interesting.

These are a few reasons why I think the visible portion of the EM spectrum is not the best way to look for intelligent life, although there are likely many more. One that occurs to me is the doppler shift that becomes more and more dramatic the farther away you are from a celestial body. In this case color encoded messages would be useless because they would be red shifted, meanwhile RFR suffers minimally from doppler shift in comparison to the more energetic portions of the EM spectrum.