On Linux, pick the color of the slider's thumbpart from the GTK theme....

chrome/common/platform_util_linux.cc

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/common/platform_util.h"
 
 #include <gtk/gtk.h>
 
 #include "base/file_util.h"
 #include "base/process_util.h"
 #include "base/singleton.h"
 #include "base/string_util.h"
+#include "chrome/browser/gtk/gtk_theme_provider.h"
 #include "chrome/common/gtk_util.h"
 #include "chrome/common/process_watcher.h"
 #include "googleurl/src/gurl.h"
 
 namespace {
 
 void XDGOpen(const std::string& path) {
   std::vector<std::string> argv;
   argv.push_back("xdg-open");
   argv.push_back(path);
@@ skipping 58 matching lines @@
                     const string16& title,
                     const string16& message) {
   GtkWidget* dialog = gtk_message_dialog_new(parent, GTK_DIALOG_MODAL,
       GTK_MESSAGE_ERROR, GTK_BUTTONS_OK, "%s", UTF16ToUTF8(message).c_str());
   gtk_util::ApplyMessageDialogQuirks(dialog);
   gtk_window_set_title(GTK_WINDOW(dialog), UTF16ToUTF8(title).c_str());
   g_signal_connect(dialog, "response", G_CALLBACK(gtk_widget_destroy), NULL);
   gtk_widget_show_all(dialog);
 }
 
-RendererPreferences GetInitedRendererPreferences() {
+RendererPreferences GetInitedRendererPreferences(Profile* profile) {
   RendererPreferences* prefs = Singleton<RendererPreferences>::get();
   static bool inited = false;
   if (!inited) {
-    gtk_util::InitRendererPrefsFromGtkSettings(prefs);
+    gtk_util::InitRendererPrefsFromGtkSettings(prefs,
+      GtkThemeProvider::GetFrom(profile)->UseGtkTheme());
     inited = true;
   }
   return *prefs;
 }
 
 }  // namespace platform_util