[sardonicism]
Why stop there? If we want a locomotive in each color scheme, why not a passenger car of each type in each paint scheme as well? Heck, why Phase III? Why not have one of each type of equipment in each paint scheme from Phase I to phase V?
In fact, let's go even further. Amtrak should also paint one of each in the color scheme of the predecessor railroads. ATSF, GN, NP, SP, NYC, SR, etc., should all be represented on Amtrak's fleet.
As a matter of fact, every single piece of equipment should be painted in a different color scheme...you know...just to please the railfans (especially those that would rather be outside taking pictures of the equipment rather than actually riding where they wouldn't be able to see the paint scheme anyway).
[/sardonicism]