Although some photographs will reproduce quite well with less than
"true color" (e.g. 256 colors), many will not..
best viewing of pictures, set your monitor at "true color"
(24-32 bit) with 800x600 screen resolution or higher. If screen images
look dark or light overall, your monitor may need adjustment/calibration. See below.
A photograph or graphic image may not
be interpreted or show properly if you have a problem with your monitor
or, it is not calibrated properly.
There are a number of
good references on the Internet if you require help with this.
PhotoShop for Photographers .
Manipulation - Timo
Autiokari, 1996-2002. Espoo City, Finland.
Denver Public Library has a page dealing with setting the
color palette, balance, brightness and contrast. Use the site
map and follow their "help" menu to "calibrating your
PCWorld article in March 2004 issue
for Color Perfection".
There are are a number of sites that
will help you determine and adjust monitor
Web Design Daily Guide
Estimating Monitor Gamma
There is also information on web
formats (gif, jpeg and png)
and others (search "graphic formats") .
Even with your monitor
calibrated, you may see images that are dark or light. However,
properly adjusting the monitor should help reduce the number of occurrences.