Source: IBM Ponder This July 2012
Problem very similar to CSE Blog: Painting Coloured Balls ( Link: http://pratikpoddarcse.blogspot.in/2010/10/painting-coloured-balls.html )
Alice picks two different random balls in and can not change their order: it colors the first in the color of the second. Bob can be color-blind: all he cares is whether a ball is colored or not; if he takes out a colored ball - he colors it again and continue. Both Bob and Alice finish their task each second.