Doubts Grasshopper

Hi Everyone, 

I have some doubt

1. Where I could change the select object color?

Always when I select something the color is white.

2. It seems that the object becomes brighter in some corners is hard to see some details. (this picture is simple, however when has more details, I can't see the elements)

(I have already tried wireframe, shaded, rendered...)

3. Finally, it is possible to select only one floor (floor, walls and ceiling) to make a simulation?