Choose WindowDisplay > Transparency
.
In the option box, adjust the sliders for the types of objects you wish to fade. 0.0000 is fully opaque; 1.0000 is fully transparent.
Transparency is achieved by blending the object color into the background color.
The values in the Control Panel update to match the current transparency levels.
Transparency can also be adjusted through the Transparency section of the Modeling or Paint Control Panel, without opening the option window.