Partially addresses #47424.

Adjusts regression fixed by https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/18786/. We were not returning the label text color correctly on the backend.

Signed-off-by: Rémy Coutable <remy@rymai.me>

The closed & backlog lists in issue boards are no collapsible. They can
be collapsed independently of each other & this selection is then saved
to the browser through localStorage. When the page loads, the code gets
the data from localStorage & determines whether to show or hide the list

Closes #23917