Bits do not naturally have Colour. Colour, in this sense, is not part of the natural universe. Most importantly, you cannot look at bits and observe what Colour they are. I encountered an amusing example of bit Colour recently: one of my friends was talking about how he'd performed John Cage's famous silent musical composition 4'33" for MP3. Okay, we said, (paraphrasing the conversation here) so you took an appropriate-sized file of zeroes out of /dev/zero and compressed that with an MP3 compressor? No, no, he said. If I did that, it wouldn't really be 4'33" because to perform the composition, you have to make the silence in a certain way, according to the rules laid down by the composer. It's not just four minutes and thirty-three seconds of any old silence.

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Now, the preceding paragraph is basically nonsense to computer scientists or anyone with a mathematical background. (My friend is one; he'd done this as a sort of elaborate joke.) Numbers are numbers, right? If I add 39 plus 3 and get 42, and you do the same thing, there is no way that "my" 42 can be said to be different from "your" 42. Given two bit-for-bit identical MP3 files, there is no meaningful (to a computer scientist) way to say that one is a recording of the Cage composition and the other one isn't. There would be no way to test one of the files and see which one it was, because they are actually the same file. Having identical bits means by definition that there can be no difference. Bits don't have Colour; computer scientists, like computers, are Colour-blind. That is not a mistake or deficiency on our part: rather, we have worked hard to become so. Colour-blindness on the part of computer scientists helps us understand the fact that computers are also Colour-blind, and we need to be intimately familiar with that fact in order to do our jobs.

The trouble is, human beings are not in general Colour-blind. The law is not Colour-blind. It makes a difference not only what bits you have, but where they came from. There's a very interesting Web page illustrating the Coloured nature of bits in law on the US Naval Observatory Web site. They provide information on that site about when the Sun rises and sets and so on... but they also provide it under a disclaimer saying that this information is not suitable for use in court. If you need to know when the Sun rose or set for use in a court case, then you need an expert witness - because you don't actually just need the bits that say when the Sun rose. You need those bits to be Coloured with the Colour that allows them to be admissible in court, and the USNO doesn't provide that. It's not just a question of accuracy - we all know perfectly well that the USNO's numbers are good. It's a question of where the numbers came from. It makes perfect sense to a lawyer that where the information came from is important, in fact maybe more important than the information itself. The law sees Colour.

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Trying to infer the Colour from the bits may seem like an okay thing to do as long as bits are tied to physical objects. You can examine a paper document and determine whether it is an original or a photocopy. You can probably examine something purporting to be a photograph and determine whether it is a photograph of a real scene, or something more complicated. But even in the analog realm, determining Colour by examination is not always possible. You can't determine by looking at a photograph of two people having sex whether they consented to the sex or not, let alone whether they consented to the making of the photograph. That's a Colour distinction that is not a function of the bits that make up the photograph - and it's true even of analog photographs.

Other important questions which you may or may not be able to answer by examining a photograph are "Are those things actually humans, or some kind of simulation?" and "How old are they?" Those questions may have been difficult with analog; they become even more difficult with digital. It is easy to imagine that someone could render by innocent means (drawing or ray tracing or whatever) an image bit-for-bit identical to an image that has the Colour (presumably Pink) of illegal child pornography. In that case, depending on your view of such things, it may matter where the bits came from to the determination of whether they are Pink (illegal) or Green (legal). Identical bits may have different Colour.

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I think computer scientists could actually understand Colour a lot better than we do, because there are places in computer science where Colour does matter. I already mentioned the idea of quoting and plagiarism - identical words are or are not okay to use without quote marks in an academic paper depending on their Colour. Those of us with degrees are able to follow the rules for that because people who aren't get kicked out of school before finishing their degrees. That's a general academic application of Colour.

If you've any exposure to metrology - not "meteorology", I mean the science of measurement - you'll be familiar with the idea of tracing the pedigree of standards. Down in the chemistry lab they have a big jar of buffer solution with a label asserting that it not only has a pH of exactly 7.00, but that its pH is "traceable" to such-and-such primary standard, through a chain that probably terminates at the National Bureau of Standards in Boulder, Colorado, USA. That's Colour. Not only do you know the pH of the buffer solution, but you know where it came from. Someone other than the National Bureau of Standards might be able to produce a buffer solution that is just as good and just as accurately 7.00 pH. If you have a sample of good pH 7.00 buffer solution it might be indistinguishable from the real traceable standard solution; but it wouldn't really be the traceable solution unless it had the intangible Colour to make it authentic.

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Random numbers have a Colour different from that of non-random numbers. The question of how to determine whether numbers are random or not by looking at them is one of the recurring flame wars of sci.crypt. You can't do it. Here's a number: 2. Was that a random number? Well, maybe I got it by rolling a die (a random generator); or maybe I got it by counting my legs (probably not random). If I give you a file of supposedly random bits, there's no way you can tell whether they are randomly generated or not. The same file could have been generated by a quantum-mechanical random source, monkeys on typewriters, or by encrypting some well-known non-random file with some scheme that may or may not be generally known.