diff --git a/development/FORMAT b/development/FORMAT
index 9ffd2926b4..0e9e95f012 100644
--- a/development/FORMAT
+++ b/development/FORMAT
@@ -7,6 +7,14 @@ changes happened in particular if possible. A good example would be
 
 -----------------------
 
+2026-07-30 Koji Yokota <yokota@lyx.org>
+	* Format incremented to 655:
+	  Support ARGB colors. \color now takes 32bit hexnames instead of 16bit
+	  in the form of:
+	     \color <#AARRGGBB> <#AARRGGBB>
+	  where the first and second arguments are light and dark colors,
+	  respectively.
+
 2026-07-24 Jürgen Spitzmüller <spitz@lyx.org>
 	* Format incremented to 654: Support some specific minted languages.
 	  - These have other names than the listings ones or are categorized as dialects.
diff --git a/lib/lyx2lyx/lyx_2_6.py b/lib/lyx2lyx/lyx_2_6.py
index 1f69a66711..68969a9191 100644
--- a/lib/lyx2lyx/lyx_2_6.py
+++ b/lib/lyx2lyx/lyx_2_6.py
@@ -1525,6 +1525,49 @@ def revert_mintedlangs(document):
             lps_res.append(l)
         document.body[k] = "lstparams \"%s\"" % ",".join(lps_res)
 
+def revert_hex32colors(document):
+    """Revert 32bit ARGB hex colors to 16bit RGB"""
+    i = 0
+    while True:
+        i = find_token(document.header, "\\color", i + 1)
+        if i == -1:
+            break
+        cn = get_quoted_value(document.header, "\\color", i, i + 1)
+
+        hex32colors = []
+        hex16colors  = []
+        hex32colors = cn.split()
+        for col in hex32colors:
+            if col.startswith("#"):
+                if len(col) == 9:
+                    hex16colors.append("#" + col[3:])
+                elif len(col) == 7:
+                    hex16colors.append(col)
+            else:
+                hex16colors.append(col)
+        document.header[i] = "\\color %s" % ' '.join(hex16colors)
+
+    i = 0
+    while True:
+        i = find_token(document.body, "\\color", i + 1)
+        if i == -1:
+            return
+        cn = get_quoted_value(document.body, "\\color", i, i + 1)
+
+        hex32colors = []
+        hex16colors  = []
+        hex32colors = cn.split()
+        for col in hex32colors:
+            if col.startswith("#"):
+                if len(col) == 9:
+                    hex16colors.append("#" + col[3:])
+                elif len(col) == 7:
+                    hex16colors.append(col)
+            else:
+                hex16colors.append(col)
+        document.body[i] = "\\color %s" % ' '.join(hex16colors)
+
+
 ##
 # Conversion hub
 #
@@ -1541,11 +1584,13 @@ convert = [
     [651, []],
     [652, [convert_removed_numeric]],
     [653, []],
-    [654, []]
+    [654, []],
+    [655, []]
 ]
 
 
 revert = [
+    [654, [revert_hex32colors]],
     [653, [revert_mintedlangs]],
     [652, [revert_specialfonts]],
     [651, [revert_numeric]],
diff --git a/src/version.h b/src/version.h
index 8b648d0726..8a494df25b 100644
--- a/src/version.h
+++ b/src/version.h
@@ -32,8 +32,8 @@ extern char const * const lyx_version_info;
 
 // Do not remove the comment below, so we get merge conflict in
 // independent branches. Instead add your own.
-#define LYX_FORMAT_LYX 654 // spitz: minted langs
-#define LYX_FORMAT_TEX2LYX 654
+#define LYX_FORMAT_LYX 655 // koji: ARGB colors
+#define LYX_FORMAT_TEX2LYX 655
 
 #if LYX_FORMAT_TEX2LYX != LYX_FORMAT_LYX
 #ifndef _MSC_VER