Demonstrating using VectorDrawable gradients to create a rainbow effect. See https://twitter.com/crafty/status/1011922414983352320

rainbow.xml

<?xml version="1.0" encoding="utf-8"?>
<!--
  Copyright 2018 Google Inc.
  Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  in compliance with the License. You may obtain a copy of the License at
  http://www.apache.org/licenses/LICENSE-2.0
  Unless required by applicable law or agreed to in writing, software distributed under the License
  is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
  or implied. See the License for the specific language governing permissions and limitations under
  the License.
  -->

<vector xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:aapt="http://schemas.android.com/aapt"
    android:width="360dp"
    android:height="208dp"
    android:viewportWidth="360"
    android:viewportHeight="208">
    <path android:pathData="M0,0 L360,0 L360,208 L0,208 Z">
        <aapt:attr name="android:fillColor">
            <gradient
                android:endX="360"
                android:endY="208"
                android:startX="0"
                android:startY="0"
                android:type="linear"
                android:tileMode="repeat">
                <item
                    android:color="#FF0064"
                    android:offset="0.0" />
                <item
                    android:color="#FF0064"
                    android:offset="0.111111" />
                <item
                    android:color="#FF7600"
                    android:offset="0.111111" />
                <item
                    android:color="#FF7600"
                    android:offset="0.222222" />
                <item
                    android:color="#FFD500"
                    android:offset="0.222222" />
                <item
                    android:color="#FFD500"
                    android:offset="0.3333333" />
                <item
                    android:color="#8CFE00"
                    android:offset="0.3333333" />
                <item
                    android:color="#8CFE00"
                    android:offset="0.444444" />
                <item
                    android:color="#00E86C"
                    android:offset="0.444444" />
                <item
                    android:color="#00E86C"
                    android:offset="0.555555" />
                <item
                    android:color="#00F4F2"
                    android:offset="0.555555" />
                <item
                    android:color="#00F4F2"
                    android:offset="0.666666" />
                <item
                    android:color="#00CCFF"
                    android:offset="0.666666" />
                <item
                    android:color="#00CCFF"
                    android:offset="0.777777" />
                <item
                    android:color="#70A2FF"
                    android:offset="0.777777" />
                <item
                    android:color="#70A2FF"
                    android:offset="0.888888" />
                <item
                    android:color="#A96CFF"
                    android:offset="0.888888" />
                <item
                    android:color="#A96CFF"
                    android:offset="1.0" />
            </gradient>
        </aapt:attr>
    </path>
</vector>