What I usually do is get the color code (#FFFFFF) from the source in my html editor (Frontpage) and copy and paste it into the color pallette of Photoshop.
I know, sometimes these will not match exactly after you import it from PS to FP.
At that point I go to (In FP) Format>Background
In the background, drop it down and click more colors. Click the 'Select' tool and it will bring up a waterdropper. glide it over your image that was created with PS and click. Now it will match exact.
Good Luck!
