Colour usage help on the command's terms, not picocli's guess

src/main/java/com/darkcollective/relix/cli/Main.java

@@ -79,6 +79,7 @@ public static int run(Host host, Interruption interruption, String... args) {
                 .setOut(out)
                 .setErr(err)
                 .setPosixClusteredShortOptionsAllowed(true)
+                .setColorScheme(CommandLine.Help.defaultColorScheme(helpColors(host)))
                 .setParameterExceptionHandler((e, ignored) -> {
                     err.print("relix: " + e.getMessage() + "\n");
                     err.print("Try 'relix --help' for more information.\n");
@@ -106,6 +107,21 @@ public static int run(Host host, Interruption interruption, String... args) {
         return status;
     }
 
+    /**
+     * Whether usage help is coloured: on the terms {@code --color=auto} colours rows, when
+     * standard output is a terminal and {@code $NO_COLOR} is not set. picocli's own
+     * detection reads the real process rather than the host, and takes an MSYS or Cygwin
+     * {@code TERM} for a terminal, so in Git Bash on Windows it coloured help written to a
+     * pipe.
+     *
+     * @param host the process
+     * @return {@code ON} or {@code OFF}, never {@code AUTO}
+     */
+    static CommandLine.Help.Ansi helpColors(Host host) {
+        return host.stdoutIsTerminal() && host.variable("NO_COLOR").isEmpty()
+                ? CommandLine.Help.Ansi.ON : CommandLine.Help.Ansi.OFF;
+    }
+
     /**
      * The command line with a bare {@code --trace} given an empty value, so that the word
      * after it is never taken for its file: {@code relix --trace q.relix} traces

src/test/java/com/darkcollective/relix/cli/command/ManagementCommandsTest.java

@@ -75,16 +75,24 @@ class Help {
         @Test
         @DisplayName("prints a command's usage to stdout")
         void command() {
-            var result = cli().run("help", "fmt");
+            var result = cli().piped().run("help", "fmt");
 
             assertThat(result.status()).isZero();
             assertThat(result.out()).startsWith("Usage: relix fmt").contains("--keywords");
         }
 
+        @Test
+        @DisplayName("colours usage on a terminal, and not in a pipe or with $NO_COLOR, wherever it runs")
+        void colours() {
+            assertThat(cli().run("help", "fmt").out()).startsWith("Usage: \u001B[");
+            assertThat(cli().piped().run("help", "fmt").out()).doesNotContain("\u001B");
+            assertThat(cli().env("NO_COLOR", "1").run("help", "fmt").out()).doesNotContain("\u001B");
+        }
+
         @Test
         @DisplayName("prints the main usage, listing every command, with no COMMAND")
         void main() {
-            var result = cli().run("help");
+            var result = cli().piped().run("help");
 
             assertThat(result.status()).isZero();
             assertThat(result.out()).startsWith("Usage: relix");

src/test/java/com/darkcollective/relix/cli/command/ScriptSourcesTest.java

@@ -110,7 +110,7 @@ void stdinWhenPiped() {
     @Test
     @DisplayName("with nothing named and a terminal on stdin, usage goes to stderr and the exit is 2")
     void nothingToRun() {
-        var result = Cli.in(dir).run();
+        var result = Cli.in(dir).piped().run();
 
         assertThat(result.status()).isEqualTo(2);
         assertThat(result.out()).isEmpty();