You will need to tell the terminal driver code that you want another
default. There exists no standard way of doing this, but in case of
Linux you have the setterm program.
"setterm" uses the information in the terminal database to set the
attributes. Selections are done like
setterm -foreground black -background white -store
where the "-store" besides the actual change makes it the default for
the current console as well. This requires that the current terminal
(TERM environment variable) is described "well enough" in the termcap
database.