Stars are "sex link" chickens, meaning they're bred specifically so that males and females are different colors when they hatch. Females are egg-laying machines that continue to lay well in the heat and cold, when many others slow down. The males are said to be good "fryers". Stars are not recognized by the American Poultry Association and are just one of many hybrid sex-link crosses available on the market today.
Red Sex-Links are the result of various crosses. White Rocks with the silver factor (the dominant white gene would produce all white offspring) are crossed with a New Hampshire male to produce the Golden Comet. Silver Laced Wyandotte crossed with New Hampshire gives the Cinnamon Queen. Two other crosses are obtained with Rhode Island White x Rhode Island Red, and Delaware x Production Red. These two crosses are simply called Red Sex-Links. Males hatch out white and, depending on the cross, feather out to pure white or with some black feathering. Females hatch out buff or red also depending on cross, and they feather out in one of three ways.
1. Buff with white or tinted undercolor (such as Golden Comet, Rhode Island Red x Rhode Island White)
2. Red with White or tinted undercolor (Cinnamon Queen)
3. Red with Red undercolor (Delaware x Production Red) (In this color pattern it is almost impossible to distinguish daughters' color from father's color.)
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I have discovered in my researching that "sex link" chickens are called by different names, so finding information about one particular kind is hard unless you know for sure who (what) the Mom & Dad are. I've also learned that sex link chickens do not breed true when breed. So if you are wanting to continue the breed you will have to find out the combination (as mentioned above) and breed from them.
As for your second question, it is recommended that you quarantine all new arrivals for a couple of months (except day old chicks) before introducing them to the other chickens. It is also recommended that the two different group be as close as possible in age or wait till the youngest ones are fully feathered and big enough to "run" or defend themselves. I have personally introduced new chickens that are a month apart in age, but I waited till the second group was fully feathered and I had them in a separate run for several weeks so that the older ones could see and "talk" to the younger ones but not able to get to them. They are all one flock now and doing just fine.