Add the monochrome android:drawable attribute to the element. For example, in res/mipmap-anydpi-v26/ic_launcher.xml
<adaptive-icon >
<background android:drawable="..." />
<foreground android:drawable="..." />
<monochrome android:drawable="@drawable/myicon" />
</adaptive-icon>
Note: If android:roundIcon and android:icon are both in your manifest, you must either remove the reference to android:roundIcon or supply the monochrome icon in the drawable defined by the android:roundIcon attribute.
