The cloud itself is actually glowing. Just like a neon sign. Here is another type of nebulae, completely different from the emission nebulae. The reflection nebulae are blue. This is because rather than emitting their own light, they are reflecting the light of the stars around them.
Reflection nebulae are blue for the same reason our sky is blue.
They reflect the light of a star. Our sky is reflecting the light of the sun, while these nebulae reflect the light of stars near them. When light passes by a particle of dust, the blue color in that light is scattered , while the rest of the colors in the light are allowed to travel undisturbed. This blue light travels around the cloud bouncing off of dust particle after dust particle until it eventually escapes the cloud and reaches our eyes. A blue nebulae is called a Reflection Nebulae.