One possible explanation may be that your image has an embedded color profile, (most browsers except IE6/7 use this now) which is not applied in dreamweaver but is used in photoshop when sampling the color.
What format are the images saved in?
Can you provide a link showing an example?
When you save for web in photoshop be sure your ICC profile selector is deselected. It can be a naughty little button.
Kevin, I am using CS4...when I save for web & devices I dont see an "ICC profile selector" to disable. Where should I be looking?