I did not try this or create the following; I'm posting it from another website for everyone's benefit.
First you'll need Phostoshop and Resorcerer. The file is located in System -> Library -> CoreServices -> Finder -> Resources and is called Finder.rsrc. The Finder is a package; control-click and choose Show Package Contents from the contextual menu. Work on a backup of the file. Open the backed up file with Resorcerer and go in the PNG type. The resources' values of what you want to change go from 5100 to 5113.[robg adds: I haven't tested this one at all, and you should exercise extreme caution if you're going to attempt it -- you're mucking about with files that the Finder needs to load in order to use properly, and one small mistake could render you Finder-less!]
You'll have to repeat it with the other gradients "1-line and 2-line" PNG resources. That's for the first thing.
- Double click on the first one, named "grey 1-line gradient" and copy all its content.
- Create a new File from Resorcerer's menu, and paste what you've just copied into this new file.
- Save it as grey 1-line.png. It's a PNG image file made with Photoshop.
- Open it with Photoshop and add it a Gradient Overlay from the Layer Style window (double click on the layer). Give it the gradient that you would like.
- Create a new layer and do a Merge Visible layers (don't flatten, you would lose the mask)
- Save it as PNG.
- Re-open the PNG file with Resorcerer and copy its data fork.
- Open the backuped Finder.rsrc, and delete the "grey 1-line gradient" resource.
- Paste what you've just copied and give it the value and the name of the prior resource.
Now, to change the little colored dots in the contextual menu, you can do the same to the resources 6203 to 6209 from this same resource. Tou can change the shape of the labels that appear in the "Preferences..." panel from the menu bar. You can also change the shape of the blue selection in the left side of the finder, when you're hovering a file onto. It's in the PICT type.
To replace the Finder.rsrc resource with the new one you've just created, go in the root account. The system will not let you replace it, since the file is in use. Even from the root. Delete it first [but don't empty the trash] and move the new one in the right place. Log out-log in.
Mac OS X Hints