GNUMERIC: setting default to "dark background + bright characters" ?

[marc dunord <marcdunord gmail com>]

dear gals/guys,

would anybody know to switch the default worksheet to "dark background
+ bright characters" in GNUMERIC ?

it's very useful if you work in dark rooms and is easier on the eyes
since it keeps the iris sphincter muscle more relaxed (which contracts
to narrow the pupil in brighter lighting).

please help!  :)

  marc