[MD History] Color tweaks.

chrome/browser/resources/md_history/history_item.html

 <link rel="import" href="chrome://resources/cr_elements/icons.html">
 <link rel="import" href="chrome://resources/html/cr/ui/focus_row.html">
 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-icon/iron-icon.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-styles/shadow.html">
 <link rel="import" href="chrome://resources/html/icon.html">
 <link rel="import" href="chrome://resources/html/util.html">
 <link rel="import" href="chrome://history/browser_service.html">
 <link rel="import" href="chrome://history/constants.html">
 <link rel="import" href="chrome://history/searched_label.html">
@@ skipping 103 matching lines @@
       }
 
       :host([selected]) #checkmark::after {
         border-color: white;
         transform: scale(1) rotate(45deg);
         /* Only animate when showing checkmark. */
         transition: transform 140ms ease-out;
       }
 
       #time-accessed {
-        color: #646464;
+        color: var(--history-item-time-color);
         min-width: 96px;
       }
 
       #domain {
         -webkit-margin-start: 16px;
         color: var(--secondary-text-color);
         flex-shrink: 0;
       }
 
       #menu-button {
@@ skipping 114 matching lines @@
           <div></div>
           <div></div>
           <div></div>
         </button>
       </div>
       <div id="time-gap-separator" hidden="[[!hasTimeGap]]"></div>
     </div>
   </template>
   <script src="chrome://history/history_item.js"></script>
 </dom-module>