The Default Shader, as do many other shaders, gives the surface colour. To mix with other shaders you need to use something like the Merge Shader, or make it a child of the a Surface Layer that has some constraints on its distribution, or attach it as a surface shader to some other shader that only applies in certain places (e.g. the Fake Stones Shader).
The reflection shader acts as a reflective coating, so existing colour will show through.
Matt