In the Apperance Tab, Choose Windows XP Style, and choose the color scheme, either Olive green, silver or blue. It will change scrollbar color along with window.
Add Custom Themes, some of them will change the color of the scroll bars.
1) Download and install StyleBuilder. The software is a 30-day trial version.
2) Open it. In the left-most side make sure blue is selected (since you don't want to change your theme).
3) In the middle of the screen you will see a window, just click on the scroll of the window, the image will be highlighted on the right-most window.
4) Now right click on the image (in the right-most pane) and edit using the 1st option.
5) You will be presented with screen like the following.
6) Paint the first three images, after which your scrollbar should look like this.
Go to the Files menu and save it. Close the editor.
7) Now you will notice that the window in the middle has a black vertical-scrollbar like this.
8) Click on Apply.
9) You will be asked to enter a name for the new style.
10) You are done. This is my "My Computer Window", see the changes. Similarly you can change the color of the horizontal scrollbar.