QBert14000
Do you have another answer for your question?
We have instruments than can measure the wavelength of the two lights as they are reflected from the screen and the overlap area where we percieve a new color will not be different to the measuring instrument and it will still only read the two original wavelengths reflecting from that overlap.
To get a better idea of the mechanics of color vision try this website
http://micro.magnet.fsu.edu/...ndcolor/humanvisionintro.html
If you would like even greater depth of explanation then there is also this website here.
NameBright - Coming Soon
And since you know you cannot see yourself,
so well as by reflection, I, your glass,
will modestly discover to yourself,
that of yourself which you yet know not of