silly question do fish change sex?

Geoff, the only ones I know of are guppies.

thank you roger the mother of this little guy has changed to black with a white stripe all the way along her body.

Cichlids that I know of do not change sex. They mature and take on adult colorations.
For instance auratus babies will all look like what a female adult looks like, yellow, black and white. When the males of the 'litter' mature they will start getting their adult colors, which differ from the females. This does not mean they are turning into males, they were always male, just not old enough to sport the adult males coloring. Hope that helps.

Geoff some females will take on darker colors with breeding and age. Not sure on these I don't keep them. It is not uncommon for cichlids to change colors.