I have a settings screen for changing the app theme at runtime. I know how to create Material design themes. I created one in my style.xml file

Here is the code for my style.xml:

 <style name="AppTheme" parent="AppTheme.Base"/>

<style name="AppTheme.Base" parent="Theme.AppCompat.Light.DarkActionBar">
        <item name="colorPrimary">@color/primaryBackground</item>
        <item name="colorPrimaryDark">@color/primaryBackground</item>
        <item name="colorAccent">@color/colorAccent</item>
        <item name="android:colorControlNormal">@color/primaryBackground</item>
        <item name="android:colorControlActivated">@color/primaryBackground</item>
        <item name="android:colorControlHighlight">@color/primaryBackground</item>
        <item name="android:textColorPrimary">@color/primaryBackground</item>
        <item name="android:textColorSecondary">@color/primaryBackground</item>
        <item name="android:windowAnimationStyle">@style/WindowAnimationTransition</item>
        <item name="android:textCursorDrawable">@drawable/cursor_indicator</item>
        <item name="windowActionBar">false</item>
        <item name="windowNoTitle">true</item>
    </style>

Now I want to change the runtime application theme from green to purple or yellow. Can anyone tell me how to create a color picker from the theme selection and how to create multiple themes in my style.xml to change it to runtime.

Have you seen this demo?

MultipleThemeMaterialDesign

Check out this class :

public class Preferences {

private static final BoolToStringPref[] PREF_MIGRATION = new BoolToStringPref[]{
            new BoolToStringPref(R.string.pref_dark_theme, false,
                    R.string.pref_theme, R.string.pref_theme_value_red),
    };

public static void sync(PreferenceManager preferenceManager) {
        Map<String, ?> map = preferenceManager.getSharedPreferences().getAll();
        for (String key : map.keySet()) {
            sync(preferenceManager, key);
        }
    }

public static void sync(PreferenceManager preferenceManager, String key) {
        Preference pref = preferenceManager.findPreference(key);
        if (pref instanceof ListPreference) {
            ListPreference listPref = (ListPreference) pref;
            pref.setSummary(listPref.getEntry());
        }
    }

/**
     * Migrate from boolean preferences to string preferences. Should be called only once
     * when application is relaunched.
     * If boolean preference has been set before, and value is not default, migrate to the new
     * corresponding string value
     * If boolean preference has been set before, but value is default, simply remove it
     * @param context   application context
     * TODO remove once all users migrated
     */
    public static void migrate(Context context) {
        SharedPreferences sp = PreferenceManager.getDefaultSharedPreferences(context);
        SharedPreferences.Editor editor = sp.edit();
        for (BoolToStringPref pref : PREF_MIGRATION) {
            if (pref.isChanged(context, sp)) {
                editor.putString(context.getString(pref.newKey), context.getString(pref.newValue));
            }

if (pref.hasOldValue(context, sp)) {
                editor.remove(context.getString(pref.oldKey));
            }
        }

editor.apply();
    }

public static void applyTheme(ContextThemeWrapper contextThemeWrapper) {
        if (Preferences.darkThemeEnabled(contextThemeWrapper)) {
            contextThemeWrapper.setTheme(R.style.AppTheme_Blue);
        }
    }

private static boolean darkThemeEnabled(Context context) {
        return PreferenceManager.getDefaultSharedPreferences(context)
                .getString(context.getString(R.string.pref_theme),
                        context.getString(R.string.pref_theme_value_red))
                .equals(context.getString(R.string.pref_theme_value_blue));
    }

private static class BoolToStringPref {
        private final int oldKey;
        private final boolean oldDefault;
        private final int newKey;
        private final int newValue;

private BoolToStringPref(@StringRes int oldKey, boolean oldDefault,
                                 @StringRes int newKey, @StringRes int newValue) {
            this.oldKey = oldKey;
            this.oldDefault = oldDefault;
            this.newKey = newKey;
            this.newValue = newValue;
        }

private boolean isChanged(Context context, SharedPreferences sp) {
            return hasOldValue(context, sp) &&
                    sp.getBoolean(context.getString(oldKey), oldDefault) != oldDefault;
        }

private boolean hasOldValue(Context context, SharedPreferences sp) {
            return sp.contains(context.getString(oldKey));
        }
    }
}

Check out the demo, which will help you learn more.