Chance is that you are yet to calibrate your monitor. Please take time to do so, at least the brightness & contrast of your monitor. Some online site provides free tools (limited, but better than not at all). My go-to site for this purpose is the one from photofriday (http://www.photofriday.com/calibrate.php).
Other possible cause is from the internet browser. I can't help you on this, but maybe others can. What browser are you using? Internet Explorer? Firefox? Opera? Chrome?
Hope this helps.
EDIT
Oops.. Sorry. You must be seeing the picture on your own monitor. Then the latter is more likely to be the cause. In this case, I can't help you much but may point you to a web search of "browser colour profile" (or somewhere around the line). Sorry, mate!