Adam,
Thanks for your reply. Your identification of the problem is exactly correct, however, I was not able to use the solution you suggested.
Modifying the icons, replacing the white background color of the icon with the transparent color on the icon left me with an icon that was totally unacceptable on a form with a black background. There are lots of pixels surrounding the icon that are near white in color. On a form with a white background this looks completely acceptable since the near white pixels blend into the white form background so that the eye does not notice them. On a form with a black background the icon appears to have a very ragged edge of white pixels and looks completely unprofessional.
What to do. Either replace the icons with ones that look good on a black form background or replace the white background of the icon with a light gray background which is what I did. With the light gray background the icon looks fine--no ragged edge--and the light gray background doesn't produce the harsh contrast that white on black produces. Thanks again for your help.
--Mike