Sometimes, Unity can’t render objects with regular shaders. When this happens, Unity renders the objects with special shaders:
The special shader that Unity uses depends on the reason that Unity can’t use the original shader.
Unity renders an object with the default error shader when there’s a problem with that object’s material or shader; for example, if no material is assigned, if the shader doesn’t compile, or if the shader isn’t supported.
Unity uses the default error shader in the Unity Editor, and in builds.
The default error shader is magenta (bright pink).
Unity renders an object with the loading shader to indicate that Unity is compiling the shader variant needed to display that object.
The loading shader is cyan (bright blue).