Simple utility that helps to create mirror enums safe for modification of the source enum.

Color.java

public enum Color {
    RED, GREEN, BLUE,;

    static {
        Mirror.of(RGB.class);
    }
}

Mirror.java

package org.enumus;

import static java.lang.String.format;
import static java.util.Arrays.stream;

public class Mirror {
    @SuppressWarnings("unchecked")
    public static <E extends Enum<E>> void of(Class<E> e) {
        Class<? extends Enum> caller = discoverCaller();
        Mirror.mirrors(caller, e);
    }

    @SuppressWarnings("unchecked")
    private static <E extends Enum<E>> Class<E> discoverCaller() {
        try {
            return (Class<E>)Class.forName(stream(new Throwable().getStackTrace()).filter(e -> !e.getClassName()
                    .equals(Mirror.class.getName()))
                    .findFirst()
                    .orElseThrow(() -> new IllegalStateException(format("Cannot discover caller's class. It seems that %s calls itself", Mirror.class)))
                    .getClassName());
        } catch (ClassNotFoundException e) {
            throw new IllegalStateException(e);
        }
    }

    public static <T extends Enum<T>, M extends Enum<M>> void mirrors(Class<T> s, Class<M> m) {
        T[] source = s.getEnumConstants();
        M[] mirror = m.getEnumConstants();
        if (source.length != mirror.length) {
            throw new IllegalStateException(format("Source and mirror enums have different number of elements: %s#%d vs. %s#%d", s.getName(), source.length, m.getName(), mirror.length));
        }
        for (int i = 0; i < source.length; i++) {
            if (!source[i].name().equals(mirror[i].name())) {
                throw new IllegalStateException(format("Element #%d of mirror %s.%s does not reflect the source %s.%s", i, m.getName(), mirror[i], s.getName(), source[i]));
            }
        }

    }
}

MyMain.java

/**
 * Simple example that  demonstrates mirror functionality. 
 * It is enough to mention the miror enum in code; its static initializer runs and invokes {@code Mirror} validator.
 * If enums are different exception is thrown.
 */
public class MyMain {
    public static void main(String[] args) {
        System.out.println(Color.RED);
    }
}

RGB.java

public enum RGB {
    RED, GREEN, BLUE,;

    static {
        Mirror.of(Color.class);
    }
}