There are two types of Nebula, bright and dark. Bright nebulas are made up of gas, dust and ice which reflect the light from adjacent stars. This might be compared to the glowing fog around a street light. When nebula is close to a large star, the intense ultraviolet light ionizes the atoms in the gases causing the cloud to glow. This is called an emission nebula. These nebula are found were stars are forming such as the Great Nebula in Orion (M42) and the Lagoon Nebula (M8).
Photograph’s of Nebulae use filters to produce colour where the filter allows the frequency to etched on the film or capture device. Reflection nebula are a cool blue colour and emiision Nebula glow red. To the human eye observing these in a telescope they only appear to be white as our eye can not detect these colours. Planetary nebula such as the Ring Nebula (M57) and the Dumbbell Nebula (M27) are the remnants of a supernova, a dying star that has created a ring of dust, gas and elements such as silica and iron, enveloping a puffed cloud around its dying form. The Veil Nebula (NGC 6960) and the Crab Nebula (M1) are both supernova remnants.
Dark Nebula is clouds made of the same materials as normal nebula but are so dense that light can not pass through it. These nebula appear to be black patches in the bright sections of the Milky Way or a light background. The Horsehead Nebula (IC 434) and the dark lane in the Lagoon Nebula (M8) are examples of a dark nebula. It is known that new stars form in these clouds through infrared telescope images.