apropos-match-face is a variable defined in `apropos.el'.
Its value is

Face for matching text in Apropos documentation/value, or nil for none.
This applies when you look for matches in the documentation or variable value
for the pattern; the part that matches gets displayed in this font.

You can customize this variable.

This variable was introduced, or its default value was changed, in version 24.3 of Emacs.