All in the Mind
There's the Home Office and the Identity and Passport Service and then there's the rest of us. An iD card is only an ID card if the IPS says it is. The cards for Foreign Nationals are actually visas. The IPS could not think of a way of storing biometrics in a foreign passport, so they came up with a plastic card and chip that repeats some of the passport info and adds on the biometric data acquired from the passport holder by IPS. Simple really, except the poor bloody foreigner now has two documents to juggle instead of one. As far as I know, every other country in the world puts visas where they belong: in passports. The US stores biometrics centrally, and uses the passport as a lookup key so that the immigration official can check the fingerprints/iris scan of the person in front of him against those on file. Every agent has a working terminal linked to a secure network. No need for biometric visas or ID cards!
The lilac and salmon card is for British citizens only, the turqoise and green is for EU citizens living in the UK (plus a few other lucky souls), and the pink and blue job is for real (non-EU) foreigners. The IPS says, mysteriously, that the turquoise and green card is for identification purposes only, leaving one to wonder what uses they see for the lilac and salmon cards other than identification. Don't worry too much, the Tories say that if they get in they will scrap the whole system. Business schools with a strong interest in IT could use it as a great case study on how not to do things.
Incidentally, I believe only the UK has a plastic card driving licence that is not really a valid driving licence without an accompanying official sheet of paper. Where do the people who design these systems come from?