On Mac OS X using the native Aqua Open Office (300m9 in my case, on Power PC
from http://ooopackages.good-day.net/pub/OpenOffice.org), open a new drawing. 
Import any bitmap graphic and make sure it is selected.  Select
tools->eyedropper.  Click on the eyedropper icon.  Move the mouse onto the
graphic. (Notice that the color next to the icon turns black as soon as the
mouse leaves the eyedropper tool window.) Click anywhere in the picture.  A
plain black color is entered into the left-hand box of the first row in the
eyedropper tool window.  This tool can then be used to replace black with
another color, but it is impossible to get any color other than black into that
left-hand box since no matter where you click on the graphic it comes up black,
and there is no way to hand-edit the color in that left-hand box.