First defined in 1975, they evolved through experience with the Experimental Packet Switched Service run by Post Office Telecommunications beginning in 1977. They were used on the SERCnet from 1980, which became the JANET academic network from 1984. The protocols gained some acceptance internationally as the first complete X.25 standard, and gave the UK "several years lead over other countries". From late 1991, Internet protocols were adopted on the Janet network instead; they were operated simultaneously for a while, until X.25 support was phased out entirely in August 1997.
Protocols
The standards were defined in documents identified by the colour of the cover:
The Pink Book defined protocols for transport over Ethernet. The protocol was basically X.25 level 3 running over LLC2.
The Orange Book defined protocols for transport over local networks using the Cambridge Ring.
The Yellow Book defined the Yellow Book Transport Service protocol, which was mainly run over X.25. It was developed by the Data Communications Protocols Unit of the Department of Industry in the late 1970s.
The Green Book defined two protocols to connect terminals across a network: an early version of what became Triple-X PAD running over X.25, and the TS29 protocol modelled on Triple-X PAD, but running over YBTS. It was developed by Post Office Telecommunications. These protocols are similar in functionality to TELNET.
The Fawn Book defined the Simple Screen Management Protocol
The Grey Book defined protocols for e-mail transfer, running over Blue Book FTP.
The Red Book defined the Job Transfer and Manipulation Protocol, a mechanism for jobs to be transferred from one computer to another, and for the output to be returned to the originating computer, running over Blue Book FTP.
The Yellow Book Transport Service was somewhat misnamed, as it does not fulfill the Transport role in the OSI 7-layer model. It really occupies the top of the Network layer, making up for X.25's lack of NSAP addressing at the time, which didn't appear until the X.25 revision, and wasn't available in implementations for some years afterwards. YBTS used source routing addressing between YBTS nodes—there was no global addressing scheme at that time.
Naming scheme
One famous quirk of Coloured Book was that components of hostnames used reverse domain name notation as compared to the Internet standard. For example, an address might be user@UK.AC.HATFIELD.STAR instead of user@star.hatfield.ac.uk.
