patch 7.4.1809
Problem:    Using wrong short option name for 'termguicolors'.
Solution:   Use the option name.
diff --git a/runtime/optwin.vim b/runtime/optwin.vim
index 7576cec..b780e03 100644
--- a/runtime/optwin.vim
+++ b/runtime/optwin.vim
@@ -414,7 +414,7 @@
 call <SID>BinOptionG("hls", &hls)
 if has("termguicolors")
   call append("$", "termguicolors\tuse GUI colors for the terminal")
-  call <SID>BinOptionG("tgc", &gcol)
+  call <SID>BinOptionG("tgc", &tgc)
 endif
 if has("syntax")
   call append("$", "cursorcolumn\thighlight the screen column of the cursor")