One of the most common issues with images here and elsewhere on the web is that the photographer is using the wrong colour space. Regardless of the space you use for editing you should always convert to SRGB when it goes on the web. Unless you are using Safari the browser will not pick up on the colour profile and therefore treat it as if it were SRGB.
To overcome the problem in Photoshop all you have to do is got to Edit, Convert (NOT asign) profile and choose SRGB.
Here's an example. This photo was edited in ProPhotoRGB. It looks nice in PS but this is how is looks if you don't convert it
![](http://ideas.pjcox.fastmail.fm/colourdemo/_STU2953darkand%20blueprophoto.jpg)
Not really what I wanted!
Things get a bit better if you convert it to AdobeRGB but not much
![](http://ideas.pjcox.fastmail.fm/colourdemo/_STU2953darkand%20blueadobe.jpg)
However for the closest match to what I intended it really needs to be converted to SRGB
![](http://ideas.pjcox.fastmail.fm/colourdemo/_STU2953darkand%20bluesrgb.jpg)
I have an action that converts the colour profile as well as convert to 8 bit and resize ready for the web.
Hope this is useful as it's a question that has been raised quite often over the years.