Change EditText hint color when using TextInputLayout

Define android:textColorHint in your application theme:

<style name="AppTheme" parent="Theme.AppCompat.NoActionBar">
    <item name="colorPrimary">@color/primary</item>
    <item name="colorPrimaryDark">@color/primary_dark</item>
    <item name="colorAccent">@color/accent</item>

    <item name="android:textColorHint">@color/secondary_text</item>
</style>

Source

Or, in your layout, like:

<android.support.design.widget.TextInputLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android.support.design:hintTextAppearance="@style/GreenTextInputLayout"
    android:textColorHint="@color/secondary_text">