The gene for fangs is recessive yet most of the dragons have fangs how can this happen

Because while fangs are receive, the lack of large teeth may cause hunting to be difficult. they might starve before maturity. also in most stories dragons are sentient, so maybe they think the lack of fangs is an unattractive feature.

the father in the first generation probably had the recessive colorblind trait in his x chromosome. if he and his wife both had the colorblind trait, even if she had 1 recessive and 1 dominant, then that trait would be passed on to their kids.

(since you didn't attach the family tree this is just an assumption)