Those are pretty typical colors -- the black will most likely disappear as he grows.
Your pond is seriously overstocked -- adding a plec to is was a bad idea on many levels. The koi alone, while small now, should be growing at an amazing rate right now if he has good water quality and proper feeding. He should outgrow your pond within a season. The plec will also outgrow your pond in very short order and, as he grows older, may very well start considering your goldfish's slime coats as a good snack. Between the growth rates and the bioload, you're beyond the edge of safety. Be sure there are plenty of plants, heavy duty filtration and that you watch your parameters very closely.
A 65 gallon pond is sufficient for a few fancy goldfish, fewer singletailed goldfish or a variety of hardy tropicals (swords, platies, wcmm, rosy barbs.....)