In visible light (right) the bright stars of the Orion nebula are hidden by dusty gas which scatters their light. Dark patches and filaments show very dense dust. The red regions are gas glowing red in the light of H&alpha at 656nm.
The infrared light (left) shines through the dusty gas, so we see the hot young stars. Here red color has been used to show the longest-wavelength infrared light, with shorter wavelengths coded by green and blue. The bluish patches show where infrared light is reflected from dust grains.
Images from NASA's Hubble Space Telescope.