How do you tell the difference between koi and golfish babies.?

My fry were laid as eggs on 19th of may, they are different sizes,the biggest is say the size of an inch and a half, they are indoors but not heated tanks, but how do i tell the diff if they are koi or goldfish, if they are goldfish they can go to new homes but if koi ill keep them, the largest is a grey colour, and most are multicoloured, none are black or just orange...i know the orange of the goldfish comes along later...i have multi coloured golfish in my 9,000 gall pond as well as multi coloured koi, does anyone know how old fry are when they start to show their koi traits on their faces...??