Why is a Screenshot a different color when dropped back in to iWeb in Safar

But I am using a websafe color 99CC99 for my background. I drop a pic on it add a dropshadow then take a screenshot with InstantShot! with about 15 pixels margin around the image. I drag it back into iWeb. It blends into the background perfectly. I publish it - it still looks perfect in Firefox and IE but in Safari the screenshot is darker and hence doesn't blend.
I've had to use Instant Alpha to remove some of the background color on the screenshots but the result is less than satisfactory.

Thanks Alancito for the response. I changed my Mac to 2.2 Gamma etc as your link suggested but it did not help. Its not really a color from monitor to monitor or monitor to printer issue.
The issue occurs because of the way Safari handles the snapshot of the section of the iWeb page - it is darker than the background therefore it doesn't blend. IE and Firefox show the blend correctly because they are ignoring the color profiles. Safari is looking for color profiles so the solution seems to be to change the snapshot color profile to match the iWeb background profile. I don't know what that is, how to do it or where to do it. Any suggestions?

Thanks, OT. I dragged the screenshot into Safari and it looks darker than the color I used for background in iWeb09. Same in Preview. I already have the optimize image box unchecked.
I've tried saving the screenshots as JPGs and PNgs but they still don't match in Safari. They match just fine in Firefox and IE.

Oh BTW - I tried jpg and png - same problem! Have to match screenshot profile to iWeb profile.