Colour science is not "frozen". Fairchild, anybody
Your point is well taken. I have Mark Fairchild's
Color Appearance Models and it is excellent. Color science is still changing and the work he and others are doing on advanced color models is really cool.
I take a 100% reflective surface and shine D65 on it measure its XYZ, call it A, and then I shine D50 on it measure its XYZ, and call it B. And A is not the same as B! These two different sets of XYZ
OK good, we agree on this; these are two sets of XYZ numbers. They are different XYZ numbers. Unanimous agreement. But the crux of the the problem is this question:
are they two different colors? Colorimetry can only answer that and other questions if we assume the same viewing conditions. XYZ coordinates are absolute, but can't really be described as
colors without more information. It they could, all our problems would be solved—we would just use XYZ coordinates anytime we wanted to communicate color.
Lets look at our people with the house again: person A inside with a tungsten light and person B outside at dusk. Now ask them this question: does the color of the lightbulb fit inside a greyscale gamut? Person A is going to say, "sure it obviously does, the color of the lightbulb is white, In our greyscale space that is around [255]." Person B is going to say, "Not so fast, that lightbulb is yellow. It lies outside the gamut greyscale." But it's the same XYZ coordinate.
If only the people could communicate the
color of the lightbulb rather than the XYZ coordinates.
They can. And this is why we have colorspaces. Both people can convert the coordinates to LAB space. To get to LAB they need to figure out a white point. Person A will use one that corresponds roughly to the 3200K tungsten and will get a LAB value like [95, 0, 0]. Person B will use a white point to something like 12000K and get a lab value [95, 0, 40].
NOW we can talk about color. Person A and B can pull up their LAB values on computer. Person A will recognize the white color as theirs and person B will identify the yellow as theirs. If they want to understand the difference between these colors they can go back to their LAB calculations where they'll see the cause of their different perceptions. They'll also see that if they want to know if it fits into a greyscale gamut, they'll also have to define that gamut in LAB or a similar space.
This is how I read your argument: There is person A inside in a well defined D50 environment. They have just decided that color A defined under D50 fits in a greyscale gamut also defined under D50. You are person B outside in the dusk screaming that color A obviously doesn't fit in a greyscale gamut. And you're right, from the point of view of person B it doesn't. But it doesn't matter. There are infinite different viewing conditions where that D50 light is not going to look white.