Note that a big part of the "black" front is the windshield, which is rendered black in those drawings. Above the windshield, the dark background makes the route display more visible. Below the windshield is an area which should be dark to prevent glare. Below that area, only version 3 is dark.

There is another reason to have a dark "forehead", which is specific for electric operation. Normally, the rearmost pantograph is raised, and, the contact strip being made of carbon, there will be abrasion which gets drawn on the front, and become quite visible.

Therefore, there are some good reasons to show dark fronts.