Don't use the ECMA standard SGR way of using bold for bright.

Working to address both fish-shell#2951 and fish-shell#3176.

src/output.cpp

@@ -70,13 +70,9 @@ static bool write_color_escape(char *todo, unsigned char idx, bool is_fg) {
         return true;
     } else {
         // We are attempting to bypass the term here. Generate the ANSI escape sequence ourself.
-        char buff[64] = "";
+        char buff[16] = "";
         if (idx < 16) {
-            // 30-37 select foreground color, 40-47 background. \e%d for dim, \e%d;1 for bright
-            snprintf(buff, sizeof buff, "\x1b[%d%sm",
-                     is_fg ? 30 + ((idx > 8) ? idx - 8 : idx) :
-                             40 + ((idx > 8) ? idx - 8 : idx),
-                     idx < 8 ? "" : ";1");
+            snprintf(buff, sizeof buff, "\x1b[%dm", ((idx > 8) ? 90 : 22) + is_fg * 10);
         } else {
             snprintf(buff, sizeof buff, "\x1b[%d;5;%dm", is_fg ? 38 : 48, idx);
         }

src/output.h

@@ -14,16 +14,16 @@
 
 /// Constants for various colors as used by the set_color function.
 enum {
-    FISH_COLOR_BLACK,
-    FISH_COLOR_RED,
-    FISH_COLOR_GREEN,
-    FISH_COLOR_YELLOW,
-    FISH_COLOR_BLUE,
-    FISH_COLOR_MAGENTA,
-    FISH_COLOR_CYAN,
-    FISH_COLOR_WHITE,
-    FISH_COLOR_NORMAL,  // the default fg color of the terminal
-    FISH_COLOR_RESET
+    FISH_COLOR_BLACK,   // 0
+    FISH_COLOR_RED,     // 1
+    FISH_COLOR_GREEN,   // 2
+    FISH_COLOR_YELLOW,  // 3
+    FISH_COLOR_BLUE,    // 4
+    FISH_COLOR_MAGENTA, // 5
+    FISH_COLOR_CYAN,    // 6
+    FISH_COLOR_WHITE,   // 7
+    FISH_COLOR_NORMAL,  // 8 terminal default
+    FISH_COLOR_RESET    // 9
 };
 
 void set_color(rgb_color_t c, rgb_color_t c2);