vector: Restore @body-font-color to black

Changed in Ica0b69ad, I presume accidentally.

https://en.wikipedia.org/w/?oldid=578807552#Font_color_of_article_text

Change-Id: I118215e7578e8af94a6909988620dcf04805d14a
(cherry picked from commit a2a76d7744e9d5fd007725ab66ab66cf002423fe)