An interesting post, my understanding is considerably more than 3% are
affected to some degree.

The 3% figure holds good for the adult male population of the United Kingdom
and the continental USA, and it is the number quoted by Ben Shneiderman in
'Designing the User Interface'. Some places have higher incidences of
dichromat colour-blindness: Wikipedia quotes an 8% figure for Australia!

I've only ever written a spectrum-shifter as bespoke code for Excel users on
a 'by request' basis and I had to work it all out from scratch - the worst
part being the need for a hand-rolled 'effective wavelength' metric for RBG
codes as perceived by healthy trichromat humans. Those neat triple
bell-curves of frequency versus sensitivity for the human retina are the
start of a very, very messy calculation.

The code is owned by a former employer of mine and will never see the light
of day again. I've asked if I can put it in the public domain and all I ever
got was boilerplate pro-forma statements about banking confidentiality and
the threat of legal action.

Anyway, your idea of a user-configurable frequency shift is an interesting
approach, and a surprisingly difficult user interface design problem: none of
the popular graphics packages (Paintshop Pro, Adobe, CorelDraw) has a colour
manipulation dialogue that does exactly what you want with images, and GIMP
has a particularly loathsome 'curves' screen under the colour tools menu.

I am not the most systematic and disciplined of beta-testers but I'd enjoy
seeing your application. I can't get at my personal mail accounts from the
trading floor, but feel free to mail me as Heffernann yah oo dot com


Regards -

Nile