The default color scheme of a GNOME terminal should change to a light background and a dark foreground. Justification: (1) This is recommended by ergonomists. (2) The current color scheme makes it just badly readable on many monitors. (3) It is used by other (GNOME) applications. (4) It is also used by for example KDE terminals, Windows telnet programs, etc. A suggestion that comes in mind is black letters on a white background...
Despite what ergonomicists may or may not say, there are many people on both sides of the dark-on-light vs light-on-dark preferences. Switching the defaults would be an arbitrary and unneeded change that would only serve to upset the half of the earth that doesn't agree with you. The important thing is that it is easy for a person who wishes to change to do so. That ability already exists in gnome-terminal.