I’ve just become aware of an interesting twist on the pink validators. If you travel between Finsbury Park and Hackney Central there are three fares. The default fares are the same as the via Highbury & Islington fares with a more expensive one via zone 1 as you’d expect.
However, there are a couple of oddities to note here. Hackney Central is effectively the same station as Hackney Downs since the link bridge was opened. And a logical route to Hackney Downs from Finsbury Park is via Seven Sisters, which of course, is in zone 3. Now there is no difference in fare between a zone 2 and a zone 2-3 journey in this case, unless you have a zone 1-2 travelcard. If you don’t touch the pink reader at Highbury & Islington then the system assumes you’ve gone via Seven Sisters and charges you a zone 3 journey.