If anything, Blue should be made a darker blue...I've always thought it was a bit light.
Yes it should, the original colors were chosen so that they would all be as distinguishable from one another as possible. The lighter blue is more distinguishable from purple than a traditional darker blue. When Lime and Coral were added this is why the deltas were added so that they could easily be distinguished from pink or yellow respectively and with lime because of it's very light color the very dark purple deltas were used. The teal they used seems to be much closer to Blue than the coral or lime are to their closest colors. While it may not seem like that big of a deal the colors are how they are identified and tracked in the system. While the chances are very slim there is the possibility that somehow the misidentification of a train compounded by a few other mistakes could somehow lead to accidents. The irony of all this is that in Disney's decision to add a close color to Blue when more distinguishable colors were available has left the monorail system to a very small degree less safe than it was before.