Judy Trogadis wrote:
>
> The paint specialist at my local hardware has just mixed a dab of green paint and a dab of red paint on a piece of paper and this resulted in a muddy brown colour. Yet, co-localization of a green fluorescent and a red fluorescent signal in a digitized image is yellow. In other words, what is the difference between a pseudocolored merged confocal image and a dab of 'merged' paint?
>

Pigments (paint) create color by subtraction. That is, they absorb some
of the light and reflect some of the light, and you see what is
reflected. As you mix different pigments, you subtract more light, so
that a mix of the primary pigments will produce black, as all of th
light is subtracted.

Your RGB display (or your multiply labeled fluorescent specimens)
produce color by addition. Addition of the three primary  colors in this
way produces white light (or more precisely, light that is perceived as
white).

--aryeh
--
Aryeh Weiss                          | email: [log in to unmask]
Department of Electronics            | URL:
http://optics.jct.ac.il/~aryeh
Jerusalem College of Technology      | phone: 972-2-6751146
POB 16031                            | FAX:   972-2-6751275
Jerusalem, Israel                    | ham radio: 4X1PB/KA1PB