Set FAB icon color

Using android:tint property you can set the color like this

<android.support.design.widget.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_gravity="bottom|end"
    android:tint="@android:color/white"
    android:src="@android:drawable/ic_input_add"
   />

UPDATE 2

If you are using com.google.android.material.floatingactionbutton.FloatingActionButton, use app:tint

app:tint="@android:color/white"

UPDATE

Refer to the answer of @Saleem Khan which is the standard way to set the app:tint using:

android:tint="@android:color/white"

via XML on FloatingActionButton.

OLD (June 2015)

This answer was written before October 2015, when android:tint on FloatingActionButton was supported only with API >= 21.

You can change it programmatically using ColorFilter.

//get the drawable
Drawable myFabSrc = getResources().getDrawable(android.R.drawable.ic_input_add);
//copy it in a new one
Drawable willBeWhite = myFabSrc.getConstantState().newDrawable();
//set the color filter, you can use also Mode.SRC_ATOP
willBeWhite.mutate().setColorFilter(Color.WHITE, PorterDuff.Mode.MULTIPLY);
//set it to your fab button initialized before
myFabName.setImageDrawable(willBeWhite);

If you are using Material Components

<com.google.android.material.floatingactionbutton.FloatingActionButton
    android:id="@+id/fab"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_margin="16dp"
    android:layout_gravity="bottom|end"
    app:fabSize="normal"
    app:tint="@color/colorAccent"
    app:srcCompat="@drawable/ic_google"/>

If you want to use icon default color, change app:tint="@null"

You have to change app:tint for that to work. android:tint didn't do any change for me.

It's easier than get the drawables, you only need to access to the color filter and set it to the color that you want.

FloatingActionButton myFab = (FloatingActionButton) findViewById(R.id.myfabid);

myFab.setColorFilter(Color.WHITE);