I don't know the exact number as to when you start or stop, but turning blue is a gradual process ranging from just a blue tint in the white name to being completely dark blue.
I once had a clanmate working towards that goal and saw there were quite a few shades between white and dark blue. I vaguely recall her end goal being something like 500-1000 recs.
255 max. You'll notice a change in color around 70-90, depending on your monitor, gamma settings, and the color of the names of the people you play near.
The only yellow titles are the ones that say "Looking for party" These are related to the party matching system (type /partymatching) to see what I mean.
The titles over people's heads that are a greenish/bluish tinge are related to clans, or their status in the game. Either the clan that they are in is level 3 or higher, or they are a noblesse.