日本の方はこちらの日本語での記事をみてください

Change the color of default folder icons in OS X Yosemite

Here is a summary of how to change the color of default folder icons in OS X Yosemite;

After your Mac restarts…

After your Mac restarts, you must see the color of default folder icons is changed! 🙂

Other System Icons

The above procedure affects only the generic folder icons and not the system ones like Application/Users/Desktop etc. In order to change these icons, the above has to be done separately. The following is a list of icns files in /System/Library/CoreServices/CoreTypes.bundle/Contents/Resources:

How to replace Yosemite icons with those from Mavericks?

If you have the icns files on Mavericks, LiteIcon allows you to replace Yosemite icons with those from Mavericks quite easily.

For Japanese

日本語が読める人はこっちの記事を読んでください。もうちょっと詳しく書いてます。

References