The skill of writing is to create a context in which other people can think.
Jeff Atwood presents a visual contrast of two WPF books in "How Not To Write A Technical Book". I haven't read either WPF book, but Jeff's post did provoke some thinking…
It's amazingly difficult to read code in monochrome these days. Language keywords, program comments, and string literals all blur into lumps. There is now chance to scan the source code for the important bits. Unfortunately, many publishers are unwilling to accept the higher cost of full color printing (except for technical books in the higher-education market, where the consumer is a PHY 101 student and at the publisher's mercy). Most college textboxes are printed in full color, but full color computer text books are a rare find.
If we look at some currently shipping WPF books, we see they are all heavily discounted from their list price and fall into the same price range:
It seems that publishers are pricing their books based on the competition and not on the production costs. Shrinking margins don't bode well for features like color.
Another topic in Jeff's post was the use of sidebars and callouts. Some people love sidebars. I don't.
A good technical book makes me think. An even better technical book makes me get to the keyboard to try something. Books with colored sidebars on every page are telling me there is something more important to read and rarely make me think or code. Instead, I'm burning cycles on context switching.
Warning: In 5 billion years, the sun will run out of hydrogen and become a red giant. Make sure your offspring will be located at a safe distance.
I see sidebars used as a copout. The author gave up trying to work an important fact into the technology's storyline, and instead threw the content inside a cartoon box. To be fair, it's not the author's fault. All publishers encourage this behavior. I think the publishers want books to look more like the web…
Books are competing with the web, to be certain. Magazines are, too. Many tech magazines are free because they are chocked full of ads. Perhaps book publishers will one day start including advertisements to offset the cost of color printing - I hope not.