First, he suggests that this is a "Stromgren" sphere (spelling uncertain). That is a sphere of Hydrogen gas that is ionized by a central star, emitting deep red (H-alpha). Outside the sphere, the radiation from the star isn't bright enough to ionize the Hydrogen, so it glows with light reflected from the star. In this image, you can see the deep red of the ionized hydrogen, and a faint white glow around this (with a slight blue cast) that is reflected light.
Second, the dust lane that extends outward from the Cocoon is dark but also bright enough to be imaged. The dust is a deep rust-red color. An analysis of the individual R, G, and B images shows that there is a thick cloud of dust at lower right (perhaps a Bok Globule?), a lane of dust that is thinner and shows some stars through it, and a light haze of red dust generally over the lower half of the image.
My goal is always to use color to reveal structure in an image, and this example is one that really does that well. This a roughly half-size version of the image. I am on the road, and I cannot post a full-size version to my web site until I return home.
author of "The New CCD Astronomy"
New Astronomy Press