[Projoy] Pedantically, RGB hex colours for Acre Street moves aren't taken from a continuous space to start with, so it isn't quite the same problem, but on the other hand, it is. As you say there are any number of ways of connecting the dots and thus of sorting. Some of these may correspond to different ways of expressing colour in N dimensions (HSV, YUV, Lab, CMYK, etc), others may be more arbitrary. In the case of CD spines, the issue is more complex because they may be printed in multiple colours, and may include special inks or other production effects that don't fit into any such colour space (metallic, dayglo, holograms, fun fur, etc), which would have to be incorporated into any sorting scheme in some (probably arbitrary) way. [rab] So don't be coy -- how did you do it?
Oooh, have I posted in here before? Not sure. Anyway... [rab, a coupla posts before, thanks for the cue] Apart from colours not existing, you're not too far off the mark, at least in the most classically accepted models... And I have a collection of 50 novels (by the one author) arranged in colour order. The trickiest bit is knowing where to start, if you're going to arrange them simply linearly. Highly recommended for displacement.
[matt, flerdle] I give in and admit that I cheated slightly. Firstly I made use of the fact that I had two shelves, one for a grayscale (black to white) and one for colours ordered roughly according to the rainbow. The difficulties you mention arose:
Spine not a single colour - resolved by choosing the 'dominant' colour.
Shiny colours/trims - like gold and silver. Basically ignored, unless the entire spine was so made at which point I think I assumed the nearest matt alternative (like yellow for gold, or gray for silver).
Colours not existing - like brown. See above. Pretend it's dark red.
So there you: Bob's yer Uncle - Job done. Interestingly I'm reminded of the time we discussed putting in for a grant to fund the development of a brown laser. However this plan was deemed to silly, and we opted to devise a photon accellerator instead.
My order jumps around a bit - some of the novels are very odd colours, but thankfully it's the one colour per book. I'm not perfectly happy with it but, given the colours they are, it's the best I could do at the time. Some of the names are misleading, but it sort of goes aqua-greenish-greenybrown-yellowish-orange-red-purplish (dark-light-dark)-darkblue-lightblue-grey-brownypinkygrey-pink-brown-chocolate.