Custom Entry control on Android

We're learning/working with Xamarin.Forms 1.3 and made a custom Android Entry renderer.
We're trying to change the color of the bottom border and nothing seems to affect it.

Here's what we tried:

nativeEditText.SetBackgroundColor (global::Android.Graphics.Color.Blue);
nativeEditText.SetHighlightColor (global::Android.Graphics.Color.Yellow);
nativeEditText.SetTextColor (global::Android.Graphics.Color.Orange);
nativeEditText.SetLinkTextColor (global::Android.Graphics.Color.Red);
nativeEditText.SetHintTextColor (global::Android.Graphics.Color.Green);

See the attached file for a visual support.

Any idea?