Can anyone explain a Box picture difference or other method to distinguish the original dark gray train rail cross track from the newer bluish gray train rail cross track? Is there a simple way to find this information? Thanks

Main difference is color and then type. 9v vs Power Functions trains after 2001 or so. 9v ended in the late 2000s. Straight PF track is hard to find since they went to that flex-track which people are "so so" on.

http://thebrickblogger.com/2011/02/lego-colors-introduction/

Also try the Lego wiki page.

I found the link above using Google. Search for Lego color differences. You can even add train to the search. Google search is helpful.