Q: How do I change Finder folder color in El Capitan

If you do want to download this, just be sure to only do it from the developer's website; do avoid these download sites as most have now begun to add unwanted ad/malware to their downloads. FWIW, the developer is a regular contributor here.

I found a solution that worked for me with El Capitan.  It's a little convoluted, but worked.  I'm only doing individual folders, not system wide.

I selected one of the blue folders and clicked on "Get Info".

I then clicked on the little icon in the upper left corner and clicked Cmd C.

I opened Photoshop Elements (assume most any photo editor should work, but not positive) and clicked File>New>Image from clipboard.  (Whatever you         need to do to get it into the program.) 

I then selected the folder and opened my color adjustment Hue/Saturation setting.  At that point, I could slide the color slider and create different colored folders.  I saved each color I liked.  Then I could Ctrl C the folder and do the 'Get Info' on the folder I wanted to change.  Click the small icon in upper left corner again and hit Ctrl V to paste the new color in.  It sometimes doesn't change immediately, but when I reboot, all the changes took place.

You've got to REALLY want to do this, but it works and once you get your colors saved, it's pretty easy to open them again and change your folder colors.

In my experience, changing folder icons or colors works with most folders except system folders. For instance, the Applications folder icon cannot be changed; however, you can change how it is displayed in the dock as it shows the icon of the first folder within the Applications folder. So, simply create an empty folder with any color/pic icon you like, name it 0 and it will show at the top.