Add correct font color override to beta variables

Note that originally the font color was specified incorrectly in
variables.less (fixed in I118215e7578e8af94a6909988620dcf04805d14a)

This restores the color to how it should be in beta
Also rename variable as the name is very misleading - it only applies
to the content

Change-Id: Iff397075ef4d11b6f815d8a596ed249d2708398a
(cherry picked from commit c6c3241806f819ae399d977fa1526450239b4898)