I found something about their genetics

the color is inherited with "incomplete dominance" (?)

the parents`s colors mix, white and red parents result in pink kids, which would themselves produce red, white and pink kids. (incomplete dominance according to Wiki...)

genetics snap dragons

my educated guess is that your friend perhaps has a kind of strain in their gardenfor some time so the genetics are kind of stable (?)

in our garden allotment-area there is a tall, mostly dark magenta flowering snapdragon with narrow reddish foliage popping up all over the place, perhaps that is a similar situation?

Anthirrinum majus seems to be a species which has been in cultivation in Europe since roughly 1500

Thanks for your reply. i think i’d prefer those dark magenta ones. These yellow-and-red ones make me think of a football team, rather than the garden of Eden, but I suppose I shouldn’t complain. They are quite hardy.

The wild species of Antirrhinum majus is pink to purple, sometimes with a yellow mouth. so yours is not an ’original species’. But the genetics of snapdragon flower colour are complicated. If you Google snapdragon genetics you’ll find they have been researched for a very long time and there's a huge amount written about them. None of which I understand.....

Thanks. I’ll get on to Google.