What I mean by homogeneous is their color...the uniform color behind the President and First Lady. The grays and whites all look very much the same over the background, and the President and First Lady stand out in vivid contrast to them.
I hope that helps!
I expect to pass through this world but once; any good thing therefore that I can do, or any kindness that I can show to any fellow creatures, let me do it now; let me not defer or neglect it, for I shall not pass this way again. Stephan Grellet