Route the COLOR format option through format_output_session (which uses
ColorMaterializer) instead of _format_plain. Previously --format color
produced identical output to --format plain because both were routed to
the same plain-text formatter. All other formats (plain, json, yaml,
rich, table) remain unaffected.
Updated CHANGELOG.md with the fix entry and CONTRIBUTORS.md with HAL 9000
contribution details.
ISSUES CLOSED: #7910
HAL9000