def Trigger = {
    final MagicColor color ->
    return new MagicWhenOtherSpellIsCastTrigger() {
        @Override
        public MagicEvent executeTrigger(final MagicGame game,final MagicPermanent permanent,final MagicCardOnStack cardOnStack) {
            return (permanent.isFriend(cardOnStack) &&
                    cardOnStack.hasColor(color) &&
                    permanent.getCounters(MagicCounterType.MinusOne) > 0) ?
                new MagicEvent(
                    permanent,
                    this,
                    "Remove a -1/-1 counter from SN."
                ):
                MagicEvent.NONE;
        }
        @Override
        public void executeEvent(final MagicGame game, final MagicEvent event) {
            game.doAction(new MagicChangeCountersAction(event.getPermanent(),MagicCounterType.MinusOne,-1,true));
        }
    };
}

[
    Trigger(MagicColor.White),
    Trigger(MagicColor.Black)
]