The Quick Reply window is designed to have it's text as a light grey to show it is disabled and when you click on the reply button, enabling the Quick Reply it is supposed to change text to Black.
Safari unfortunately doesn't support this change (hopefully in Tiger, with the new WebKit). If you want to see how it is supposed to work, try Firefox as it does it correctly. It's a feature used in several websites.
I still remember Macnutt.