You probably already have it. Look in the folder where you've installed your JDK - for example, C:\Program Files\Java\jdk1.6.0_11. One of the files should be called either src.zip or src.jar. Either way, you can copy this file to another directory, then unzip it, or unjar it using
java -xvf src.jar .
Once it's unzipped/unjarred - there are all the JDK library source files, right there. Well, not really all of them, because they exclude native methods and some packages like the com.sun.* stuff. But most classes of interest are there, including java.awt.Color. Enjoy.