The Old man breeder will tell you one of your Pokmon seem special and that you should hold onto it IF you try to breed a shiny with a non-shiny Pokmon. This is implemented as it wouldn't be balanced if people would try to get a rare shiny such as Charmander by breeding that with a common shiny from the same egg group. It could potentially cause an inflation and ruin the market. Thus, it is ONLY possible to breed a Shiny Pokmon with a Shiny Pokmon in PokeMMO - If both parents are Shiny, the child will now always be Shiny (and hatch as the same species as the female parent).