[Patch] Update previews correctly with color changes

[Yuri Lensky <ydl@ydl.cm>]

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The hash computed for LaTeX previews did not actually take into account the
true foreground/background text color, so org would not refresh previews
when themes change.

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From dbecdbb6f3cc5f9b6d094310ecdd6c5aedfe5505 Mon Sep 17 00:00:00 2001
From: "Yuri D. Lensky" <ydl@Yuris-MacBook-Pro.local>
Date: Wed, 24 Feb 2021 12:40:25 -0800
Subject: [PATCH] lisp/org.el: Update previews correctly when color chnages.

* lisp/org.el (org-format-latex): When computing a hash that
determines if a preview needs to be re-generated, use the actual color
of the face rather than just the setting symbol.
---
 lisp/org.el | 22 ++++++++++++++++------
 1 file changed, 16 insertions(+), 6 deletions(-)

diff --git a/lisp/org.el b/lisp/org.el
index 7d8733448..4ae604fe6 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -15965,15 +15965,25 @@ Some of the options can be changed using the variable
 			 (fg
 			  (let ((color (plist-get org-format-latex-options
 						  :foreground)))
-			    (if (and forbuffer (eq color 'auto))
-				(face-attribute face :foreground nil 'default)
-			      color)))
+                            (if forbuffer
+                                (cond
+                                 ((eq color 'auto)
+                                  (face-attribute face :foreground nil 'default))
+                                 ((eq color 'default)
+                                  (face-attribute 'default :foreground nil))
+                                 (t color))
+                              color)))
 			 (bg
 			  (let ((color (plist-get org-format-latex-options
 						  :background)))
-			    (if (and forbuffer (eq color 'auto))
-				(face-attribute face :background nil 'default)
-			      color)))
+                            (if forbuffer
+                                (cond
+                                 ((eq color 'auto)
+                                  (face-attribute face :background nil 'default))
+                                 ((eq color 'default)
+                                  (face-attribute 'default :background nil))
+                                 (t color))
+                              color)))
 			 (hash (sha1 (prin1-to-string
 				      (list org-format-latex-header
 					    org-latex-default-packages-alist
-- 
2.24.3 (Apple Git-128)