If patterned backgrounds are used, they have to allow for
content reading without catching the eye's attention. One should not forget that
the background is a medium to help reading and facilitate the content's
comprehension.
The more color contrast, the more comfortable the reading.
The highest contrast is achieved by using a white background and black letters.
Although it has a lot of contrast, the opposite combination (black background
and white letters) is not so widely used. Forums have discussed which of the two
options is better for reading texts. In my opinion, it is important to keep in
mind the type of site to develop and its target audience when deciding on the
contrast. If we want to create a site for skaters, rock'n roll fans, bikers,
etc., then a black background would be preferred. For corporate sites,
intranets, banking sites, etc., I recommend using a white background with black
letters. In the same Web application environment, to vary the background's
color, it is always recommended to keep light or pastel colors and letters in
dark colors, like black or close shades of black.
There are sites where you can try some color combinations
for background and text online. One of them is http://www.nbp.org/ic/nbp/process.html?mv_nextpage=customize%2ehtml&mv_todo=set&style_size=large&id=EcfxrsZw
If you'd like to read about research done on this topic, I
recommend http://www.usabilitywebsite.com/usabilityresearch_color.htm
With GeneXus 8.0 you can set color combinations in the
topic editor, under "Form" class, and play around without having to change a
single line of code.
There are a couple of text colors that have a particular
meaning, regardless of what the text says. Therefore, one should use those
colors only for that specific meaning and, conversely, to get such particular
meaning use those colors only: Red and blue.
Red means attention, error, danger (it also applies to a
physical environment, such as the "stop sign"), therefore, it should only be
used for error messages. When showing an error message in a color other than
red, the user will have a more difficult time to identify this text as such
(sometimes attention icons are used, but what is recommended and most widely
used is the red color).
Blue, generally seen with an underlined text, is used to
show a link.
If within a text there is a blue word, intuitively one
tends to think that it is a link (even if it's not underlined), and the user is
disappointed if s/he clicks on that word and it doesn't go anywhere.
Oftentimes links
within text blocks are shown in the same color as the text itself, with
underlining. This may also be thought of as a link, although it's not as
effective as using the blue color code. Therefore, I recommend no underlining in
texts. If you'd like to highlight something in a text block, it is best to use
bold letters.
Source http://www.grokdotcom.com/usability-of-color.htm