Think about Octorox,

If Lucas was really trying to make the films look truer to Ralph McQuarrie's original art, He would have replace things with CGI models more like Ralph McQuarrie's original art. also If Lucas was really trying to make the films look truer to the color of the Ralph McQuarrie's original art, He would have use a CGI lighting program like "shake" to change the color and lighting.

The real reason for the bad color in the 04 DVDs is to hide things.
Just go into photoshop (which seems like the program Lucasfilm used on the 04 DVDs) and lighten up some scenes of the 04 DVD and you we see it is the same cleanup as the SE 1997.
The 2004 DVDs is just the 1997 SE with somethings added.
Lucas just messed with the color to make it look newer.
It was NOT to make the films look truer to Ralph McQuarrie's original art.

The 2004 DVDs are just a cheap photoshop made rip-off.