The Cornish Cross took over the chicken meat industry back in the mid 20th century. Since then different companies have developed and refined their own version of Cornish Cross. It took years of careful breeding to develop them, they are not a simple cross of two breeds.
You can get a decent meat chicken by crossing a Rock with a Cornish. They will not grow nearly as fast or as big as a Cornish Cross, they will grow more like a dual purpose chicken. The Cornish heritage should give them more breast meat than most dual purpose chickens. Feather color can affect the appearance of the carcass if you pluck instead of skin. Darker pin feathers are easier to see. I skin mine so feather color isn't important.