HAVENT read it yet but how does one baby have orange eyes when they have red and green eye...

For one it is fictional and two, gene magic.
You not heard of certain traits skipping generations e.g. red hair because the gene combo just magically worked out that way?

Or black babies being born to white couples because they inherited certain genes and when the two made a baby, boom, all the cherries lined up

There's more sciency ways to put it but it's really not deep :L
The human race is just a weird hodge podge of proteins and water

It was a rhetorical question