An excellent companion-read to the linked article is: http://ansuz.sooke.bc.ca/entry/23 http://ansuz.sooke.bc.ca/entry/23 It builds up a concept of "Colour" as

An excellent companion-read to the linked article is: http://ansuz.sooke.bc.ca/entry/23 http://ansuz.sooke.bc.ca/entry/23 It builds up a concept of "Colour" as describing information about a thing (distinct from metadata / tagging) which is not necessarily derivable from the thing itself. Most frequently it uses the term to describe provenance, but is careful not to limit the concept. To quote the ansuz' essay above in relation to the linked article: When we use Colour like that to protect ourselves against viruses or malicious input, we're using the Colour to conservatively approximate a difficult or impossible to compute function of the bits. Either our operating system is infected, or it is not. A given sequence of bits either is an infected file or isn't, and the same sequence of bits will always be either infected or not. Disinfecting a file changes the bits. Infected or not is a function, not a Colour. The trouble is that because any of our files might be infected including the tools we would use to test for infection, we can't reliably compute the "is infected" function, so we use Colour to approximate "is infected" with something that we can compute and manage - namely "might be infected". Note that "might be infected" is not a function; the same file can be "might be infected" or "not (might be infected)" depending on where it came from. That is a Colour. Once you've left your computer alone with a potential adversary, it has the might-be-compromised Colour. Proving whether it definitely has or has not been compromised is easy for devices which do not have this Colour, but as described in the linked-to article, very difficult or impossible once it has this Colour.