@badge-bg should be @gray-light not #f5f5f5

customize.html

@@ -920,7 +920,7 @@ lead: Customize Bootstrap's components, LESS variables, and jQuery plugins to ge
           <input type="text" placeholder="#fff">
           <p>Badge text color</p>
           <label>@badge-bg</label>
-          <input type="text" placeholder="@gray-lighter">
+          <input type="text" placeholder="@gray-light">
           <p>Badge background color</p>
           <label>@badge-link-hover-color</label>
           <input type="text" placeholder="#fff">

dist/css/bootstrap.css

@@ -4075,7 +4075,7 @@ a.thumbnail:focus {
   text-align: center;
   white-space: nowrap;
   vertical-align: middle;
-  background-color: #f5f5f5;
+  background-color: #999999;
   border-radius: 10px;
 }
 

less/variables.less

@@ -379,7 +379,7 @@
 @badge-color:                 #fff;
 @badge-link-hover-color:      #fff;
 
-@badge-bg:                    #f5f5f5;
+@badge-bg:                    @gray-light;
 @badge-active-color:          @link-color;
 @badge-active-bg:             #fff;