I was puzzled by this. I'm wondering whether a certain degree of colour contrast is required by the new Rail Vehicle Accessibility regulations [RVAR], but I haven't found anything so far.
This document shows the exemptions from RVAR that LT have got for the new trains:http://www.uk-legislation.hmso.gov.uk/si/si2008/em/uksiem_20082969_en.pdf
However, the colour schemes on the Victoria Line are nowhere near as annoying at the [RVAR mandated ?] announcements at refurbished Northern Line stations that tell you the next station - ON BITS OF THE LINE WHERE THE NEXT STATION IS NEVER DIFFERENT!!!
Maybe for the benefit of partially sighted people ?