Signal-Android/app/src/main/res/drawable/contact_selection_checkbox.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item android:state_checked="true" android:state_enabled="false">
        <layer-list>
            <item>
                <shape android:shape="oval">
                    <solid android:color="@color/core_grey_25" />
                    <stroke android:width="2dp" android:color="@color/white" />
                </shape>
            </item>
            <item android:drawable="@drawable/ic_check_outline_22" />
        </layer-list>
    </item>
    <item android:state_checked="true">
        <layer-list>
            <item>
                <shape android:shape="oval">
                    <solid android:color="@color/core_ultramarine" />
                    <stroke android:width="2dp" android:color="@color/white" />
                </shape>
            </item>
            <item android:drawable="@drawable/ic_check_outline_22" />
        </layer-list>
    </item>
    <item android:state_checked="false">
        <color android:color="@null" />
    </item>
</selector>