patch 8.0.0142
Problem:    Normal colors are wrong with 'termguicolors'.
Solution:   Initialize to INVALCOLOR instead of zero. (Ben Jackson, closes
            #1344)
diff --git a/src/syntax.c b/src/syntax.c
index 75ede36..b2108e4 100644
--- a/src/syntax.c
+++ b/src/syntax.c
@@ -8765,6 +8765,10 @@
 	else
 	{
 	    vim_memset(&new_en, 0, sizeof(new_en));
+#ifdef FEAT_TERMGUICOLORS
+	    new_en.ae_u.cterm.bg_rgb = INVALCOLOR;
+	    new_en.ae_u.cterm.fg_rgb = INVALCOLOR;
+#endif
 	    if (char_attr <= HL_ALL)
 		new_en.ae_attr = char_attr;
 	}