Not sure what your screenshot is of. 4 is just barely brighter. Not much at all. Almost like an accident.
In this pic, 4 is on the left, and most definitively has a darker border around the input field. It is actually, lighter (just barely) than 3 (on right).
As a web designer, 4 is driving me nuts. Stuff is so far apart. First, if you only have a couple tabs open, you have to move your mouse quite a long way to select the tabs. When they are limited to a certain size like in 4, then mouse movement is much more efficient. Plus, the new tab button is ridiculously far away. It's all just poor design 101. Apple used to be great at design and communication flow, but lately their apps have started putting buttons in every corner of the window. Truth is, it started with the dock. I'm mousing all over the dang screen. Uppder left for apple menu, then bottom left for system prefs, then upper right for volume, then bottom right for trash. There is absolutely no reason all the system functions can't be in the same place. At least windows has all the switching and system functions at the bottom, and program menus at the top. They even have a arguably better concept of putting the program menus within each individual window. People from windows don't grasp at all what is going on with apple's windows and dock. In Windows, the start bar has a button for everything running. And every window has it's own set of of menus. That rant over, that's the only thing windows does better.
Also in Safari 4, why have they made the refresh button part of the field for the url field window? All the way to the right? Argh. Once again, stuff scattered all over creation. Some command buttons on the left, refresh on the right (and really tiny!).
There's a screen in final cut that has this affliction that kills me every time. Add master template. It's a big resizeable window. In the bottom right is the ok or add buttons. Upper left you choose from differnent template designs, and bottom left is cancel. So depending on your window size, the ok and cancel buttons are potentially 2 feet apart!
Rant over for now.
Edit: Wait, also in the Safari 4 top sites window... search is bottom right. Edit is bottom left. And of course you just clicked the icon at upper right to get to the window. Are they trying to give us carpel tunnel or what? There are very basic design screwups that beginners make. Like a powerpoint made by a receptionist.