Aloha,
Wow you hatched a divers group of eggs. But congrats on your new additions!
EE birds are just a Russian Roulette of mystery. Because they either come in homozygous and heterozygous forms of the egg color. Meaning they are not always true blue egg colored producers. They are precrossed with other birds from the hatchery. Often times getting birds that are in essence the look of an EE but not producing the desired egg color, hints the name "Easter Egger". Hens are easy to determine if they carry the trait for blue eggs. But that is when they lay their first egg. If it is a Roo, unless you know a geneticist and willing to pay the fee, then you can tell it for sure.
But testing through breeding can determine certain truths about your EE Roo and the EE gals too.. Which you did by hatching babies. If the babies from that EE X EE mating are female and lay the colored eggs when they begin then you can assume they are Homozygous ("O,O") and or Heterozygous ("O,o") for the blue egg gene. But if you have a hen from that mating lay an egg outside of that color blue zone. Like a Brown, tinted, & white. Then you can assume that both parents carries an allele (gene) for that egg color which makes both parents Heterozygous (O,o) for the blue egg color . But again with the males, they may carry the recessive (o,o), less dominant gene. Known as Homozygous receive.
But you will know for sure when the chicks get to laying age. But that is on a minor scale.
Now since you did the other mating with other hens, this could give you the answer to your roo. If he is the Homozygous for the egg color, or at least a Heterozygous one, it will show. But you would need other produced hens to be sure of it. But I digress, the other hens are Brown layers. So when a blue layer crosses with the Brown layer you should get a Green colored layer. Which means the shell is blue and the brown is incorporated on the shell. (Still reading up on it but I know we have a geneticist person on here to give you an accurate deduction. This is just what I know from my own crossing/reading)
But to have 3 black chicks, when you have a Golden Comet, I can only think that it is because the egg you picked up for hatching was either from the Barred rock and on or the Australorp. But you just have to wait till that chick grows. But when you breed a Red roo to a Barred hen you will have a sex-linked chick. Meaning the boy chicks will have a spot on head and the girl chick will be black with some brown on their head. SO I do believe you have a Roo chick there.
If you can post pics then everyone can help. OMG I wrote alot hope it helps a little......
