cmdutils: add -colors option

cmdutils.c

@@ -1518,6 +1518,18 @@ int show_filters(void *optctx, const char *opt, const char *arg)
     return 0;
 }
 
+void show_colors(void *optctx, const char *opt, const char *arg)
+{
+    const char *name;
+    const uint8_t *rgb;
+    int i;
+
+    printf("%-32s #RRGGBB\n", "name");
+
+    for (i = 0; name = av_get_known_color_name(i, &rgb); i++)
+        printf("%-32s #%02x%02x%02x\n", name, rgb[0], rgb[1], rgb[2]);
+}
+
 int show_pix_fmts(void *optctx, const char *opt, const char *arg)
 {
     const AVPixFmtDescriptor *pix_desc = NULL;