Barnacles and hybrids

the Humber Barnacle Goose flock contains 3 hybrid type birds; one is large and with grey-brown in the plumage and appears to be a Greylag / Barnacle hybrid as odd broods have been seen in most years; the other two are quite similar with a lot of Barnacle characters and are Barnacle sized and with a similar jizz but are they hybrids or birds with a plumage pigment problem? and if hybrids with what;