Why are the colours of nebulae different?

[Mekon]

When I view the Orion Nebula through my telescope it appears a grey (US 'gray') cloud. When I take a time exposure photograph I can see purple and and green clouds.
1. Why is it different?
2. If i were in a spaceship and much closer, would I see the colours one sees in the beautiful Hubble images?

TIA
Mekon

[Chronos]

Two answers: chemical composition of the gas clouds and emission frequency of illumination sources. Photography reveals light frequencies inaccessible to the human eye.

[Drakkith]

Almost all nebulae are gray in the eyepiece due to the human eye being unable to detect color in such low light levels. Even going close would not look quite like the hubble images. They simply don't put out that much light.

Also, many of the images seen where there are very bright distinct colors are false color images. These are taken through narrowband filters designed to isolate a very small wavelength range and are then assigned a specific color in the final image. For example, the Hubble typically uses Red for Sulfur emissions, Green for Hydrogen, and Blue for Oxygen. However both Sulfur and Hydrogen emit their light in the Red area of the spectrum, while Oxygen emits it's light in between green and blue.

[Mekon]

Thanks for both replies. :)