Shade Smooth and holes I'm quite new to Blender and I have a problem when I'm using Shade Smooth. As soon as I am shade smoothing The object with the hole in it, there are some weird color changes around the hole. It doesn't change in the rendered image. 
The holes where made with the boolean modifier. Am I doing it the wrong way or is there a way to fix this?
Avoid boolean to create holes in a mesh. It will always create really bad topology and then when you apply subdivision and smooth shade, everything is going to fail.