How do I change the texture preview window?

Looking at this tutorial:

https://anonym.to/?https://youtu.be/OWtQnZsSdEU?t=15m20s

I realize that his texture preview window has two different dark grey squares, and he can see the sprite without any problem.

I'm using unity 5.5.0 and my squares are white and light grey, making me really difficult to see anything in there.

On the sprite editor I can change this squares colors but not in the texture importer or the texture renderer. Is there any way to achieve this change on this texture importer and texture renderer preview window?

 

To clarify more my question. This two pictures have the same sprite loaded:

This is what I got:


And this is what I want: