long exposure strange colours issue...from viewfinder

Ironheart

From the D800 manual, page 106:
Close the Viewfinder Eyepiece Shutter
When taking photos without your eye to the viewfinder, close the viewfinder eyepiece shutter to prevent light entering via the viewfinder from appearing in photographs or interfering with exposure

Rx4Photo

From my experience making the mistake of leaving the Viewfinder Eyepiece Shutter open, it's essentially a light leak situation - always seems to ruin the lower half of the image.