Terminal color

Fastmash uses a small terminal palette to make human-readable output easier to scan. Help headings use bold default foreground; Commands, options and Operation names use cyan. Advisory findings use yellow. Errors, Refusals, Internal failures and violations of supplied Health expectations use red. Descriptions, values and examples keep the default foreground. Every style uses the terminal’s default background, and wording carries the meaning when styling is disabled.

The controls select whether eligible presentation is styled:

fastmash --color=auto --help
fastmash --color always --help
fastmash --no-color --help
fastmash --color=never --help

auto is the default. Each destination is checked separately: redirecting stdout does not disable eligible stderr styling, and redirecting stderr does not disable eligible stdout styling. Redirected output, failed terminal detection, TERM=dumb and a nonempty NO_COLOR disable automatic styling, including bold. An empty NO_COLOR permits automatic styling. always overrides these checks, including for redirected presentation. never and --no-color suppress every generated style.

Fastmash-authored failure diagnostics style only the existing program prefix, such as fastmash:, in red. The prefix resets before the diagnostic body, so multiline messages, hints and input bytes retain their default foreground. Errors, Refusals and Internal failures share this failure role while keeping their distinct text and exit statuses. Stderr eligibility controls the prefix independently of stdout; a calculation piped to another program can still show colored diagnostics in a terminal. Diagnostics forwarded from child programs retain their existing bytes. Styling uses fixed sequences and does not require allocating a new diagnostic message, including the low-memory fallback. If argument collection fails before option scanning begins, no invocation control has taken effect; that early fallback uses the default automatic stderr policy.

Readable Table health reports style their existing headings in bold, advisory markers in yellow and declared violation markers in red. A finding’s structured basis selects its marker; labels or samples containing those words do not receive color. Each heading and marker resets immediately, leaving counts, observations, Field names and examples plain. Color preserves the report contents and validation status: advisory findings can remain yellow when validate succeeds. See Table health reports for the distinction between inference and supplied Health expectations.

Only help, Fastmash’s failure prefix and readable Table health reports are eligible presentation surfaces. Calculation results, Dataset comparison reports, copied Records, CSV, health TSV and version output retain their original bytes even with --color=always. Color never decorates data or changes exit status.

Color controls require their exact spellings. Repeated controls follow the last one reached by ordinary option scanning. As with existing options, -- ends scanning and POSIXLY_CORRECT stops it at the first operand. Help and version terminate scanning immediately, so place color controls before them:

fastmash --no-color --color=always --help
fastmash --color=always --help > help.txt

The palette and stream handling follow the CLI Guidelines, and environment suppression follows the NO_COLOR convention, with explicit invocation controls taking precedence. Fastmash also suppresses bold whenever styling is disabled.