I was surprised by the comment in this thread about rendering intent, particularly perceptual and relative colorimetric, not being covered well anywhere. I would suggest "Real World Digital Photography," 2nd edition, by Katrin Eismann, Sean Duggan, and Tim Grey (yes, this goes back to 2004), p. 622, for an excellent one-paragraph description with what happens with the two intents when moving from one color space to another. For an even more nuanced understanding of the implications, one can go to two books by Martin Evening, "Adobe Photoshop 7.0 for Photographers" (an oldie-but-goodie from 2002), p.92-93, and "Adobe Photoshop CS5 for Photographers," (2010) pp.670-673. I do know there is much to be gained from reading about a difficult or technical topic in more than one treatment of it. So we could definitely look forward to how Jeff distills this. Nevertheless, there is good material out there on this.
I'll add a way of looking at this which actually sounds like an approach Jeff would enjoy using to describe these rendering intents (he could give me credit!): If we think of a map of the United States as a map of a color space, and everything out of the U.S. as an out-of-gamut color, then with Relative Colorimetric, everything outside of the U.S. gets put in the same place (same color) as the nearest point at the U.S. border. So Mexico City and Sao Pauo both get mapped to a U.S. border city, appearing with the same color as those border cities, and Paris becomes the same color as a city on the U.S. eastern seaboard. And nothing changes within the map. With Perceptual, when we want to incorporate out-of-gamut colors (out-of-the-U.S. cities), we compress the locations of existing cities in the U.S. and bring the foreign cities in, maintaining some separation, and therefore the perceptual differences between them, but at the expense of some shift in what started out as in-gamut (in-map). This gives a worse-than-deserved rap to Relative Colorimetric, as our out-of-gamut colors in photography won't be as out-of-gamut as Sao Paulo or Paris are to the U.S. But I think this is an interesting way of visualizing what happens. Photography is fun! --Barbara