Android spinner custom

I'm trying to make a custom Spinner on android. so I can add a white arrow (This is achieved with android: drawableEnd) but what I can not do is paint the right part of the spinner blue.

The spinner is custom so

android:id="@+id/text1"
style="?android:attr/spinnerItemStyle"
android:singleLine="true"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ellipsize="marquee"
android:background="@drawable/badge_circle_gris"

android:drawableEnd="@drawable/prueba"

And the backgraund

<solid
    android:color="@color/gris_claro"
    ></solid>
<padding
    android:left="1dip"
    android:right="1dip"
    android:top="1dip"
    android:bottom="1dip" />
<corners android:radius="15dp"/>

in the backgraund try to do gradient instead of solid but it does not stay as I want. Attached photo of the desired result.