I don't know whose idea it was, however the FT has fought two court case at least to seek to prevent other publishers using pink stock for city pages - one with the Evening Standard which is lost and the Standard proceeded to print its city pages on pink page and one with an indian publisher.  The FT failed to establish the pink coloured paper as a signficant enough to trademark. 

As an aside in the late 90's the sister site FT.com was blocked by the networks of some City banks on the basis that the pages contained so high a percentage of flesh pink that the blocking software deemed them pornographic.