Merge branch 'jk/ref-filter-colors-fix'

Merge branch 'jk/ref-filter-colors-fix'

This is the "theoretically more correct" approach of simply
stepping back to the state before plumbing commands started paying
attention to "color.ui" configuration variable.

Let's run with this one.

* jk/ref-filter-colors-fix:
  tag: respect color.ui config
  Revert "color: check color.ui in git_default_config()"
  Revert "t6006: drop "always" color config tests"
  Revert "color: make "always" the same as "auto" in config"