Source code for built-in shaders

Questions & Answers
1

Which one should I start from?

  1. The official package: UnityBuiltinShaders.zip

  2. What seems to be the latest: http://unity3d.com/download_unity/builtin_shaders.zip

2

Built-in shaders for current and past Unity versions can be downloaded from the Download Archive page: http://unity3d.com/unity/download/archive