Reflection Nebulae

Reflection nebulae are formed by scattering and reflecting the light of surrounding stars by gas and dust clouds. The radiation from these stars is not energetic enough to ionize the interstellar medium and create an emission nebula.
Reflection nebulae often appear bluish because blue light is scattered better than red light. Depending on the spectral class of the illuminating stars as well as additional interstellar dust, yellowish nebulae can also be formed.