What changes were made to Maersk blue?
Considering that color has been produced explicitely and exclusively for Maersk sets, it's highly unlikely they would change it. Most people seem to agree that the same color has been used for all Maersk ships sets.

That said, you'll also need to consider that even if LEGO never intended to change the color, small variations in hue are always possible (red and purple are much more susceptible to this). Also, in the case of Maersk, LEGO used their entire supply in 2006 and said at the time that they wouldn't issue Maersk sets again because of that. However, Maersk realized the demand was high (LEGO did consider making a version fo the ships in another color altogether at some point) and agreed to have LEGO make a new batch to later on. So these are in effect different batches, separated by a few years, which means any hue change will be more likely to be noticed than if it appeared gradually over time.