There is one face from the Helm package that is meant to highlight the
matches of a grep or grep-like command (‘ag’ or ‘ripgrep’). It is
helm-grep-match. However, this face can only apply when the user does
not pass ‘--color=always’ as a command-line option for their command.
Here is the docstring for that face, which is defined in the helm-grep.el library (you can always visit the source code with M-x find-library).
Face used to highlight grep matches. Have no effect when grep backend use “–color=”
The user must either remove ‘--color’ from the flags passed to the grep
function, or explicitly use ‘--color=never’ (or equivalent). Helm
provides user-facing customization options for controlling the grep
function’s parameters, such as helm-grep-default-command and
helm-grep-git-grep-command.
When ‘--color=always’ is in effect, the grep output will use red text in
bold letter forms to present the matching part in the list of
candidates. That style still meets the contrast ratio target of >= 7:1
(accessibility standard WCAG AAA), because it draws the reference to
ANSI color number 1 (red) from the already-supported array of
ansi-color-names-vector.