attrs.xml

<resources>
    <declare-styleable name="ThemeableMediaRouteButton">
        <attr name="iconColor" format="reference|color" />
    </declare-styleable>
</resources>

menu_cast.xml

 <menu xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto" >
 
    <item
        android:id="@+id/menu_cast_item"
        android:orderInCategory="0"
        app:showAsAction="always"
        app:actionProviderClass="com.ryanharter.mediaroute.widgets.ThemeableMediaRouteActionProvider"
        android:title="@string/menu_cast"/>
 </menu>

styles.xml

<resources>
    <style name="Widget.MediaRouter.MediaRouteButton" parent="Widget.MediaRouter.Light.MediaRouteButton">
        <item name="iconColor">@color/red</item>
    </style>

    <style name="Widget.MediaRouter.MediaRouteButton.Section1">
        <item name="iconColor">@color/white</item>
    </style>

    <style name="Widget.MediaRouter.MediaRouteButton.Section2">
        <item name="iconColor">@color/blue</item>
    </style>
</resources>

ThemeableMediaRouteActionProvider.java

package com.ryanharter.mediaroute.widgets;

import android.content.Context;
import android.support.v7.app.MediaRouteActionProvider;
import android.support.v7.app.MediaRouteButton;

/**
 * A MediaRouteActionProvider that allows the use of a ThemeableMediaRouteButton.
 */
public class ThemeableMediaRouteActionProvider extends MediaRouteActionProvider {

    public ThemeableMediaRouteActionProvider(Context context) {
        super(context);
    }

    @Override public MediaRouteButton onCreateMediaRouteButton() {
        return new ThemeableMediaRouteButton(getContext());
    }
}

ThemeableMediaRouteButton.java

package com.ryanharter.mediaroute.widgets;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.PorterDuff;
import android.graphics.drawable.Drawable;
import android.support.v7.app.MediaRouteButton;
import android.util.AttributeSet;

import com.ryanharter.mediaroute.R;

/**
 * Allows theming of the MediaRouteButton using the theme associated with 
 * the context passed in.
 */
public class ThemeableMediaRouteButton extends MediaRouteButton {

    private final int color;
    private Drawable originalDrawable;

    public ThemeableMediaRouteButton(Context context) {
        this(context, null);
    }

    public ThemeableMediaRouteButton(Context context, AttributeSet attrs) {
        this(context, attrs, R.attr.mediaRouteButtonStyle);
    }

    public ThemeableMediaRouteButton(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);

        TypedArray a = context.obtainStyledAttributes(attrs,
                R.styleable.ThemeableMediaRouteButton, defStyleAttr, 0);
        color = a.getColor(R.styleable.ThemeableMediaRouteButton_iconColor, 0);
        a.recycle();

        applyColorToRemoteIndicator();
    }

    private void applyColorToRemoteIndicator() {
        if (originalDrawable == null) {
            return;
        }
        originalDrawable.setColorFilter(color, PorterDuff.Mode.SRC_ATOP);
        setRemoteIndicatorDrawable(originalDrawable);
    }

    @Override
    public void setRemoteIndicatorDrawable(Drawable d) {
        // save the original icon used by MediaRouterButton to tint it later
        originalDrawable = d;
        super.setRemoteIndicatorDrawable(d);
    }
}

themes.xml

<resources>
    <style name="Theme.MyApp">
        <item name="mediaRouteButtonStyle">@style/Widget.MediaRouter.MediaRouteButton</item>
    </style>
 
    <style name="Theme.MyApp.Section1">
        <item name="mediaRouteButtonStyle">@style/Widget.MediaRouter.MediaRouteButton.Section1</item>
    </style>
 
    <style name="Theme.MyApp.Section2">
        <item name="mediaRouteButtonStyle">@style/Widget.MediaRouter.MediaRouteButton.Section2</item>
    </style>
</resources>