startop/apps/ColorChanging/app/src/main/res/layout/activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/button"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="16dp"
        android:onClick="goRed"
        android:text="red"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button4"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:onClick="goYellow"
        android:text="YELLOW"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button6"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="16dp"
        android:layout_marginLeft="16dp"
        android:layout_marginTop="32dp"
        android:onClick="goGreen"
        android:text="GREEN"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button" />

    <Button
        android:id="@+id/button7"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="165dp"
        android:layout_marginLeft="165dp"
        android:layout_marginTop="115dp"
        android:layout_marginEnd="165dp"
        android:layout_marginRight="165dp"
        android:onClick="goViolet"
        android:text="VIOLET"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.428"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button8" />

    <Button
        android:id="@+id/button10"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="165dp"
        android:layout_marginLeft="165dp"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="165dp"
        android:layout_marginRight="165dp"
        android:onClick="goBlue"
        android:text="BLUE"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button8" />

    <Button
        android:id="@+id/button8"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="165dp"
        android:layout_marginLeft="165dp"
        android:layout_marginTop="16dp"
        android:layout_marginEnd="165dp"
        android:layout_marginRight="165dp"
        android:onClick="goOrange"
        android:text="ORANGE"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

    <Button
        android:id="@+id/button11"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="32dp"
        android:layout_marginEnd="16dp"
        android:layout_marginRight="16dp"
        android:onClick="goIndigo"
        android:text="INDIGO"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button4" />

    <Button
        android:id="@+id/button12"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="162dp"
        android:layout_marginLeft="162dp"
        android:layout_marginTop="25dp"
        android:layout_marginEnd="161dp"
        android:layout_marginRight="161dp"
        android:onClick="goCyan"
        android:text="CYAN"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button7" />

    <Button
        android:id="@+id/button13"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="162dp"
        android:layout_marginLeft="162dp"
        android:layout_marginTop="25dp"
        android:layout_marginEnd="161dp"
        android:layout_marginRight="161dp"
        android:onClick="goBlack"
        android:text="BLACK"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/button12" />
</androidx.constraintlayout.widget.ConstraintLayout>