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

chrome/common/platform_util.h

 // 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.
 
 #ifndef CHROME_COMMON_PLATFORM_UTIL_H_
 #define CHROME_COMMON_PLATFORM_UTIL_H_
 
 #include "app/gfx/native_widget_types.h"
 #include "base/string16.h"
 #include "chrome/common/renderer_preferences.h"
+#include "chrome/browser/profile.h"
 
 class FilePath;
 class GURL;
 
 namespace platform_util {
 
 // Show the given file in a file manager. If possible, select the file.
 void ShowItemInFolder(const FilePath& full_path);
 
 // Open the given file in the desktop's default manner.
@@ skipping 17 matching lines @@
 // whether the view has the visible attribute set.
 bool IsVisible(gfx::NativeView view);
 
 // Pops up an error box with an OK button. If |parent| is non-null, the box
 // will be modal on it. (On Mac, it is always app-modal.) Generally speaking,
 // this class should not be used for much. Infobars are preferred.
 void SimpleErrorBox(gfx::NativeWindow parent,
                     const string16& title,
                     const string16& message);
 
-RendererPreferences GetInitedRendererPreferences();
+RendererPreferences GetInitedRendererPreferences(Profile* profile);
 
 }
 
 #endif  // CHROME_COMMON_PLATFORM_UTIL_H_