patch 8.2.0906: when setting 'termguicolors' SpellBad is no longer red Commit: https://github.com/vim/vim/commit/ea563cc22be043ff91dcbdf2878c3d1fd944e573 Author: Bram Moolenaar <Bram@vim.org> Date: Fri Jun 5 19:36:57 2020 +0200 patch 8.2.0906: when setting 'termguicolors' SpellBad is no longer red Problem: When setting 'termguicolors' SpellBad is no longer red. Solution: Only use the RGB guisp color for cterm when using the "underline" or "undercurl" attributes to avoid the background color to be cleared. Also make t_8u empty when the termresponse indicates a real xterm. (closes #6207)

--- a/src/term.c
+++ b/src/term.c
@@ -4819,6 +4819,11 @@ not_enough:
 			if (version < 95)
 			    is_not_xterm = TRUE;
 
+			// With the real Xterm setting the underline RGB color
+			// clears the background color, disable "t_8u".
+			if (!is_not_xterm && *T_8U != NUL)
+			    T_8U = empty_option;
+
 			// Only request the cursor style if t_SH and t_RS are
 			// set. Only supported properly by xterm since version
 			// 279 (otherwise it returns 0x18).