IMO VW used half black headrests to improve visibility to the front by rear
passengers. It's the same philosophy behind using half black sunvisors. Of
course, some people do not like the multi colored headrests. Therefore, the
single color gray (or beige) headrest may have been nothing but a styling
exercise (black being the exemption since it was the German version of a
"universal match"). Just look at most German dashes. They are usually black
even in multi-hued interiors.

BenT