How Do We See Violet? Understanding Wavelengths

[Fridgefox]

I don't understand how we see violet. We have cones sensitive to red, blue and green and so can see these primary colours. Colours with wavelengths between these are seen when more than one cone is stimulated. How can we see a colour of shorter wavelength than blue? Surely it ought to stimulate the blue-sensitive cone only and therefore be seen as blue. Can anyone help?

 

[mfb]

We have cones sensitive to red, blue and green

That is an oversimplified description how our eyes work. We have three different types of sensors, with a different sensitivity in some broad frequency (or "color") range. Based on their signals, the brain can find some interpretation about the color of incoming light.
Violet can correspond to a significant excitation of "blue", with nearly no excitation of the others, for example. "Blue" would be seen by the other sensors, too. See this diagram from wikipedia:

http://upload.wikimedia.org/wikipedia/commons/0/04/Cone-fundamentals-with-srgb-spectrum.svg

 

[Borek]

I didn't know M & L responses are that similar.