[quote]wavelength of visible light is indeed ~400 to 700 nm [/quote]

The correct statement should be :
The wavelength of visible light [b]in vacuum[/b] is between 400-700 nm.
From my personal point of view: wavelength is not a good indicator for light
because it has different value when travel in different meterial.
Frequency should be a better parameter to specify light/electromagnetic wave.

However, people used to refer to vialble light with wavelength (wavelength of light in vacuum.)