Change the color of a specifed region
void SLsmg_set_color_in_region (color, r, c, dr, dc)
int color;
int r, c;
unsigned int dr, dc;
SLsmg_set_color_in_region may be used to change the color of a
rectangular region whose upper left corner is given by
(r,c), and whose width and height is given by dc
and dr, respectively. The color of the region is given by the
color parameter.
SLsmg_draw_box, SLsmg_set_color