Liz Elliott of Biotele.com says "magenta ain't a color."
[W]hat does the brain do when our eyes detect wavelengths from both ends of the light spectrum at once (i.e. red and violet light)? Generally speaking, it has two options for interpreting the input data:
a) Sum the input responses to produce a colour halfway between red and violet in the spectrum (which would in this case produce green – not a very representative colour of a red and violet mix)
b) Invent a new colour halfway between red and violet
Magenta is the evidence that the brain takes option b – it has apparently constructed a colour to bridge the gap between red and violet, because such a colour does not exist in the light spectrum. Magenta has no wavelength attributed to it, unlike all the other spectrum colours.