With standing straight up with a flat face, only light coming in from behind will show it. That is why all 'target' pistol sights are either straight up or angled back slightly, so the front sight (the important sight) is flat black on a white target face. Note all aperture sights - hooded globes to eliminate any light from shining on the front sight be it a blade, cross hairs or aperture - always flat black on a white target with black centre.
Trouble is, we don't always shoot at white targets and sometimes we need to 'see' the front sight superposed on that target. Shooting a black sight at a black target is very difficult, but if it picks up some light, placing that white or yellow dot or circle on the black target is easy. Only a flat, angled surface gives true or almost true light reflection.
Some guys will slot the rear face of the front blade and glue in a strip of ivory into the slot. Others use an angled bead with round notch rear, or V rear, or shallow Express-type V as on the rifle in the picture above.
An excellent rear sight for use with a bead, is a deep U notch, where the bead sits in the bottom of the U and giving equal light on the bottom and sides. This sight is aimed as if it was an aperture rear sight and works for many people, including Mark, who has won the ALR Chunk Shoot 2 years in a row. this sight would also be a good hunting sight, with the bead in the bottom for point blank shooting, and raised level with the top of the U for longer range, ie: a 150 yard zero.