What is the difference between a dark reflecting nebula and light relfecting nebula?

A nebula is a region of interstellar gas and dust. Dark nebulae such as the Horsehead Nebula are so dense that they block light from other sources, such as background emission nebulae, reflection nebulae, or other stars.

Other types of nebulae do reflect light. Emission nebulae are clouds of ionized gas that allow red, blue, and violet light through. Generally, these nebulae appear reddish.

Reflection nebulae are clouds of dust that simply reflect light from nearby stars. The dust particles of reflection nebulae usually only scatter blue light, so the appearance is blue.