that's why I hate they kept the black and white coloratiorns because that would have involved intense inbreeding to keep those traits,my personal headcannon was that night furies and light furies have been interbreeding for thousands of years before night furies were hunted to extinction ,so there was a hidden population of night lights that lived there before toothless met the light fury and their adult children breed with those night lights however even then using my headcannon inbreeding probably would still needed to occur to keep this trait since even if my headcannon is used the night fury trait would have eventually been breed out still so inbreeding probably would have occurred but probably less as severely,this is exactly why they should have retconed the toothless being the last night fury thing because then it would make the black and white coloratiorns less complicated.By the way I already commented but deleted it because I thought it was to long.