XmGetColors takes a screen, a colormap, and a background pixel, and returns pixel values for foreground,
select, and shadow colors.
screen Specifies the screen for which these colors should be allocated.
colormap Specifies the colormap from which these colors should be allocated.
background
Specifies the background on which the colors should be based.
foreground
Specifies a pointer to the returned foreground pixel value. If this argument is NULL, no value
is allocated or returned for this color.
top_shadow
Specifies a pointer to the returned top shadow pixel value. If this argument is NULL, no value
is allocated or returned for this color.
bottom_shadow
Specifies a pointer to the returned bottom shadow pixel value. If this argument is NULL, no
value is allocated or returned for this color.
select Specifies a pointer to the returned select pixel value. If this argument is NULL, no value is
allocated or returned for this color.