public Map<Colore, List<Forma>> colore2forme() {
        Map<Colore, List<Forma>> colore2forme = new HashMap<>();
        List<Forma> tmp= null;
        for(List<Forma> forme : this.livello2forma.values()){
            for(Forma forma : forme){
                tmp=colore2forme.get(forma);
                if(tmp==null)
                    tmp=new ArrayList<>();
                tmp.add(forma);
                colore2forme.put(forma.getColore(), tmp);
            }
        }
        return colore2forme;
    }