Digital photos and colour differentiation.

[Tool]

Is it just me, or have you noticed that a digital photo of a section can really show up colour differences that are not so apparent directly?

[GnomeKing]

(welcome to the darkside)

...

[John Wells]

Your camera can record a higher contrast image than you see, especially if you up some of the settings (eg contrast / vividness). However, it is best to do this on the computer with the normal image.
The camera can also see more of the spectrum than your eyes, both at the near infra-red and UV ends.

Sometimes, it is advantageous to remove one or two colour channels (a simple click in Photoshop or equivalent) from an image, eg just using the blue channel if you want stones emphasised in a green landscape:
http://www.armadale.org.uk/phototech01.htm

See the last 3 images on http://www.armadale.org.uk/phototech04.htm of the Sutton Hoo Excavation in 1985, where Christopher Brooke has heavily tweaked a UV image.
When delineating a site in an aerial photo, realism is less important than seeing what is there. In that respect, some applications of aerial photography are more akin to a geophysical survey.
The image below, by Jim Knowles, is an example of a carefully processed near infra-red image:


When working outside the visible spectrum, photo realism has no meaning.