To complete Sunit's answer, you can use a selector, not to the text string but to the textColorHint. You must add this attribute on your editText:
android:textColorHint="@color/text_hint_selector"
And your text_hint_selector should be:
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item android:state_focused="true" android:color="@android:color/transparent" />
<item android:color="@color/hint_color" />
</selector>