terminal-util: get_color_mode checks COLORTERM

src/basic/terminal-util.c

@@ -1278,6 +1278,11 @@ ColorMode get_color_mode(void) {
                         /* We only check for the presence of the variable; value is ignored. */
                         cached_color_mode = COLOR_OFF;
 
+                else if (STRPTR_IN_SET(getenv("COLORTERM"),
+                                       "truecolor",
+                                       "24bit"))
+                        cached_color_mode = COLOR_24BIT;
+
                 else if (getpid_cached() == 1)
                         /* PID1 outputs to the console without holding it open all the time.
                          *

src/basic/terminal-util.h

@@ -100,16 +100,19 @@ typedef enum AcquireTerminalFlags {
 /* Limits the use of ANSI colors to a subset. */
 typedef enum ColorMode {
         /* No colors, monochrome output. */
-        COLOR_OFF = 0,
+        COLOR_OFF,
 
         /* All colors, no restrictions. */
-        COLOR_ON  = 1,
+        COLOR_ON,
 
         /* Only the base 16 colors. */
-        COLOR_16  = 16,
+        COLOR_16,
 
         /* Only 256 colors. */
-        COLOR_256 = 256,
+        COLOR_256,
+
+        /* For truecolor or 24bit color support.*/
+        COLOR_24BIT,
 
         _COLOR_INVALID = -EINVAL,
 } ColorMode;