1/ dont think there is any true randomness in drop coz implementing true random numbers isnt that easy andcheap to set in logical systems.
2/ wondering wht would happen if one player will lvl up to lets say 10th lvl with killing only 0 % drop chance enemies, thus no bosses, to eliminate possibility of pink drop. And then just with 4 other same guys will go kill some good drop boss. Do you still think that chance that they will all get pink will be like 0.000000001? I think it will be much more i dare to say around 33.3-%