Most applications use blue as their central color, particularly business applications (e.g. Windows uses blue in most of it's chrome). I am being pushed to use purple throughout our current application (because that is the color of the business logo) but I think it looks more professional in shades of blue, so I need to argue my case (more eloquently than saying 'purple sucks'). Is the preference for blue perhaps a cultural thing or physiological thing (i.e. less taxing on the rods/cones in the eye)? Why is blue preferred over purple?
"Blue, often associated with stability, symbolizes trust, wisdom and confidence. Blue has been shown to produce a calming effect and is often used to promote products and services related to cleanliness. More accepted by males than females, it is a preferred color for corporate America."
From http://www.pallasweb.com/color.html: "•Purple: creativity, mystery, (reddish purple) royalty, mysticism, rarity. Purple is associated with death in Catholic cultures, as mentioned above. •Blue: loyalty, security, conservatism, tranquility, coldness, sadness. Light blues create a feeling of openness, clean air and freshness, while dark blues can convey tradition, trust and solidity."
It all depends what you want to convey with your site!
Blue is the color of communication.
Blue is also a color that isn't effected by color blindness, or at least not as often as red-green.