It can be: Pg Ml Co. Is confirmed in scientific literature for one line of andalusian blue chickens.
But since you can't get double lacing on blue, that would work too: Pg Ml co+ (no Columbian)
Pg or Ml alone could work also.
Pg alone is no melanizer so you might lack pigment for a decent lace.
Other melanizers could jump in though.
The following is hypothetical:
Co could be a factor to clean up specks of black in the blue.
Dominant white is also a flecky color and is improved by the columbian factor i.m.o.
But since you can't get double lacing on blue, that would work too: Pg Ml co+ (no Columbian)
Pg or Ml alone could work also.
Pg alone is no melanizer so you might lack pigment for a decent lace.
Other melanizers could jump in though.
The following is hypothetical:
Co could be a factor to clean up specks of black in the blue.
Dominant white is also a flecky color and is improved by the columbian factor i.m.o.
