I think that someone who has even done the Master-Cleanse for 40 days might not have a perfectly pink tongue. It just varies..I haven't heard of many people getting a totally pink tongue after any amount of fasting.
In my experience - I did a 9day Master-Cleanse - white tongue the whole time. A couple of months later (after many b&p's) I did a 6day MC...started white then on Day6 it really did pink right up (evenly)...although not perfectly pink.