ChromeOS OOBE: Update Welcome screen colors after UI review.

chrome/browser/resources/chromeos/login/oobe_a11y_option.html

 <link rel="import" href="chrome://resources/html/polymer.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/iron-flex-layout/classes/iron-flex-layout.html">
 <link rel="import" href="chrome://resources/polymer/v1_0/paper-toggle-button/paper-toggle-button.html">
 
 <dom-module name="oobe-a11y-option">
   <template>
     <style>
       :root {
           --oobe-toggle-button-size: {
             box-shadow: 0 1px 3px 0 rgba(0, 0, 0, 0.4);
             height: 16px;
             top: -2px;
             width: 16px;
           };
           --oobe-toggle-bar-size: {
             height: 12px;
             left: 4px;
             width: 24px;
           };
+          --paper-toggle-button-checked-bar-color: var(--google-blue-500);
           --paper-toggle-button-checked-bar: var(--oobe-toggle-bar-size);
           --paper-toggle-button-checked-button: {
             @apply(--oobe-toggle-button-size);
             transform: translate(14px, 0);
           };
+          --paper-toggle-button-checked-button-color: var(--google-blue-500);
+          --paper-toggle-button-checked-ink-color: var(--google-blue-500);
           --paper-toggle-button-label-spacing: 0;
           --paper-toggle-button-unchecked-bar: var(--oobe-toggle-bar-size);
           --paper-toggle-button-unchecked-button:
               var(--oobe-toggle-button-size);
       }
     </style>
     <link rel="stylesheet" href="oobe_a11y_option.css">
     <div id="elementBox" class="layout horizontal">
       <div class="flex layout vertical center-justified">
         <div id="titleContainer">
           <content select=".title"></content>
         </div>
         <div class="display-value" hidden="[[!checked]]">
           <content select=".checked-value"></content>
         </div>
         <div class="display-value" hidden="[[checked]]">
           <content select=".unchecked-value"></content>
         </div>
       </div>
       <paper-toggle-button id="button" checked="{{checked}}"
           aria-label$="[[labelForAria]]">
       </paper-toggle-button>
     </div>
   </template>
 </dom-module>