"rgb, hex, cmyk"
Those things are approximations of what actually goes into a color....rgb is an especially detestable way to go about arriving at a color Red, Green, Blue only can go so far in constructing subtleties, Cyan, Magenta, Yellow, Black....quite a bit better, Hex, still a maybe....
Part of the problem here also is we're dealing with solid color, so then there's density thing.....the above systems are meant to work out shadings, lighter color areas, shadowing.....usually not just a block of color.....
A Pantone Matching color would get very close & account for "Darker does not mean more red" and possibly even "Metamerism" darker could mean more blue, but then what form of blue? maybe more black, in combination with a different base red.....
Computer monitors are notorious for being "off" in a number of ways & playing one person's setup against another's only compounds the problem....I could give you a very accurate NUMBER, as I see in a very flat, uninhibited way after years of use of the color matching system, but that would still involve monitors which basically fucks the whole deal.......
Hey Marty....how many Red Master Touch / One Touch Pluses do you have anyway?