You can use a drawable as the text colour, and in drawable you can use selector to select the colour according to enabled status. Using following drawable definition as colour will make your disabled menu items grey and the rest black.
In e.g. res/drawable/default_text_colour.xml
:
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_enabled="false" android:color="@android:color/darker_gray"/>
<item android:color="@android:color/black"/>
</selector>
Then, using the drawable:
<item name="android:textColor">@drawable/default_text_colour</item>