Don't set meta `theme-color` by default (#24340)

Fixes https://github.com/go-gitea/gitea/issues/24321. By not setting
this meta tag, Safari will use body color for chrome and out-of-viewport
areas, which looks much better then static mismatching green.

As per
[MDN](https://developer.mozilla.org/en-US/docs/Web/HTML/Element/meta/name/theme-color)
it's really only Apple browsers who still support this tag, most others
have dropped support.

4 files changed, 6 insertions, 7 deletions

diff --git a/custom/conf/app.example.ini b/custom/conf/app.example.ini
index 29ebb4699b..144691c00c 100644
--- a/custom/conf/app.example.ini
+++ b/custom/conf/app.example.ini
@@ -1203,10 +1203,9 @@ ROUTER = console
 ;; Number of line of codes shown for a code comment
 ;CODE_COMMENT_LINES = 4
 ;;
-;; Value of `theme-color` meta tag, used by Android >= 5.0
-;; An invalid color like "none" or "disable" will have the default style
-;; More info: https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android
-;THEME_COLOR_META_TAG = `#6cc644`
+;; Value of `theme-color` meta tag, used by some mobile browers for chrome and
+;; out-of-viewport areas. Default is unset which uses body color.
+;THEME_COLOR_META_TAG =
 ;;
 ;; Max size of files to be displayed (default is 8MiB)
 ;MAX_DISPLAY_FILE_SIZE = 8388608
diff --git a/docs/content/doc/administration/config-cheat-sheet.en-us.md b/docs/content/doc/administration/config-cheat-sheet.en-us.md
index 772e0535e9..74110ea443 100644
--- a/docs/content/doc/administration/config-cheat-sheet.en-us.md
+++ b/docs/content/doc/administration/config-cheat-sheet.en-us.md
@@ -220,7 +220,7 @@ The following configuration set `Content-Type: application/vnd.android.package-a
 - `SHOW_USER_EMAIL`: **true**: Whether the email of the user should be shown in the Explore Users page.
 - `THEMES`:  **auto,gitea,arc-green**: All available themes. Allow users select personalized themes.
   regardless of the value of `DEFAULT_THEME`.
-- `THEME_COLOR_META_TAG`: **#6cc644**:  Value of `theme-color` meta tag, used by Android >= 5.0. An invalid color like "none" or "disable" will have the default style.  More info: https://developers.google.com/web/updates/2014/11/Support-for-theme-color-in-Chrome-39-for-Android
+- `THEME_COLOR_META_TAG`: **\<empty\>**: Value of `theme-color` meta tag, used by some mobile browers for chrome and out-of-viewport areas. Default is unset which uses body color.
 - `MAX_DISPLAY_FILE_SIZE`: **8388608**: Max size of files to be displayed (default is 8MiB)
 - `REACTIONS`: All available reactions users can choose on issues/prs and comments
     Values can be emoji alias (:smile:) or a unicode emoji.
diff --git a/modules/setting/ui.go b/modules/setting/ui.go
index 90bad50d3b..bf2b2d4bb7 100644
--- a/modules/setting/ui.go
+++ b/modules/setting/ui.go
@@ -77,7 +77,7 @@ var UI = struct {
 	GraphMaxCommitNum:   100,
 	CodeCommentLines:    4,
 	ReactionMaxUserNum:  10,
-	ThemeColorMetaTag:   `#6cc644`,
+	ThemeColorMetaTag:   ``,
 	MaxDisplayFileSize:  8388608,
 	DefaultTheme:        `auto`,
 	Themes:              []string{`auto`, `gitea`, `arc-green`},
diff --git a/templates/base/head.tmpl b/templates/base/head.tmpl
index 3932a58598..cd9bbed444 100644
--- a/templates/base/head.tmpl
+++ b/templates/base/head.tmpl
@@ -5,7 +5,7 @@
 	<meta name="viewport" content="width=device-width, initial-scale=1">
 	<title>{{if .Title}}{{.Title | RenderEmojiPlain}} - {{end}}{{if .Repository.Name}}{{.Repository.Name}} - {{end}}{{AppName}}</title>
 	{{if .ManifestData}}<link rel="manifest" href="data:{{.ManifestData}}">{{end}}
-	<meta name="theme-color" content="{{ThemeColorMetaTag}}">
+	{{if ThemeColorMetaTag}}<meta name="theme-color" content="{{ThemeColorMetaTag}}">{{end}}
 	<meta name="default-theme" content="{{DefaultTheme}}">
 	<meta name="author" content="{{if .Repository}}{{.Owner.Name}}{{else}}{{MetaAuthor}}{{end}}">
 	<meta name="description" content="{{if .Repository}}{{.Repository.Name}}{{if .Repository.Description}} - {{.Repository.Description}}{{end}}{{else}}{{MetaDescription}}{{end}}">