use ColorPropType everywhere there is a color prop on TextInput

Summary:
If using colors that are not strings react native would warn you of the problem. I made some changes so color props use `ColorPropType` instead of `PropTypes.string`.
Closes #8325

Differential Revision: D3475516

Pulled By: javache

fbshipit-source-id: b7e40a0de5e665fc5f41a975650bbba0ec210814

Author: erickreutz

Libraries/Components/TextInput/TextInput.js

@@ -11,6 +11,7 @@
  */
 'use strict';
 
+var ColorPropType = require('ColorPropType');
 var DocumentSelectionState = require('DocumentSelectionState');
 var EventEmitter = require('EventEmitter');
 var NativeMethodsMixin = require('NativeMethodsMixin');
@@ -269,7 +270,7 @@ var TextInput = React.createClass({
     /**
      * The text color of the placeholder string
      */
-    placeholderTextColor: PropTypes.string,
+    placeholderTextColor: ColorPropType,
     /**
      * If true, the text input obscures the text entered so that sensitive text
      * like passwords stay secure. The default value is false.
@@ -278,7 +279,7 @@ var TextInput = React.createClass({
     /**
     * The highlight (and cursor on ios) color of the text input
     */
-    selectionColor: PropTypes.string,
+    selectionColor: ColorPropType,
     /**
      * See DocumentSelectionState.js, some state that is responsible for
      * maintaining selection information for a document
@@ -336,7 +337,7 @@ var TextInput = React.createClass({
      * The color of the textInput underline.
      * @platform android
      */
-    underlineColorAndroid: PropTypes.string,
+    underlineColorAndroid: ColorPropType,
   },
 
   /**