I'm confused.. I thought leghorns were used to cross to create hybrids, but the leghorn breed is not itself a hybrid. Am I incorrect?
The leg horn is a breed, and not a hybrid. However, there are many colors, and even 2 comb styles (rose comb and straight comb) accepted in the SOP. There are even bantam leghorns.
Many different breeds are used to produce production hybrids, or sex links. Leghorn is only of many breeds that can be used.