This tip works if you use SafariStand. SS offers an option to change the metal texture of Safari, giving you three shades from which to choose (light, medium and dark). The problem is that with Safari 4 the tabs don't match the main windows when you use this feature.
Since I prefer the dark theme, I thought I could dig into Safari's Resources folder (/Applications/Safari.app/Contents/Resources/) and find the PNG files Safari uses for the tabs and simply change their brightness to match the main window. After some tweaking, I got what I feel is a much nicer GUI. See the screenshot and see what you think. Safari 4 was just way too dark for my tastes.
The only problem is that when Safari is in the background the tab doesn't match the main window, but I can live with it until I have the time to fix it.
This is fairly easy to do with any image editor. The files are PNG, so you don't need Photoshop. Just adjust the brightness to match the shade you want. It will take a few trials and some error. The files that affect the active tab when Safari is active are:
AW ActiveTabFill.png
AW ActiveTabLeftCap.png
AW ActiveTabRightCap.png
I would like to have a script or small app to automate this for folks, but I just don't have the time currently.