There's a couple ways to go when breeding red sex links. They don't breed true, since they are mutts, but you'll get the most consistent looking chicks if you put a red rooster over them. Most of the chicks will be reddish, some with mixes of white feathering and then you'll get the occasional white chick with black spots or white to a few red spots.
The most consistent would be a red. However, you could use just about any rooster, if you don't care. Using a Sex Link male will not assure you of uniform chicks. In fact, you'll get a real mix of things, but a lot of white.