* src/dialog-cell-format.c (create_coloring_page): Now, the
method to find out whether a cell has been colored or not
is to compare the RGB values to zero.
Commented out the attachment of background_radio_list
because the functionality is not ready yet.

* src/dialog-cell-format.c (apply_coloring_format): Added support
for background solid coloring. Howver, changes to the style of
the cells in this regard have no effect in the display. The reason
for this is unknown to me as of now.