No, the screen size did not change at all from 5th Gen to 5.5 Gen. What they changed was to go with a brighter screen that used less power.
I have not seen any indication by Apple's marketing weasels on the web pages going on about a better, bigger, brighter, more colorful, etc. screen, so I am assuming that is uses the same screen as the 5.5Gen iPods.
I figure if it had more colors or something like that, that would be one of the new and improved features they would be going on about.
Patrick