patch 7.4.1781
Problem:    synIDattr() does not respect 'guicolors'.
Solution:   Change the conditition for the mode. (Christian Brabandt)
diff --git a/src/eval.c b/src/eval.c
index a3fe2a2..b3ebbd7 100644
--- a/src/eval.c
+++ b/src/eval.c
@@ -20019,8 +20019,8 @@
     }
     else
     {
-#ifdef FEAT_GUI
-	if (gui.in_use)
+#if defined(FEAT_GUI) || defined(FEAT_TERMTRUECOLOR)
+	if (USE_24BIT)
 	    modec = 'g';
 	else
 #endif