I'm not a fan of spray-can finishes, as I have trouble getting away from bubbles and spatter. Yellowing should be of little concern, as it would not seem likely to show on brass. We live near salt water and have brass numbers on the house. Last time I finished them, about 4 yrs. ago, I used clear polyurethane. The secret is to clean them immaculately with brass polish, degrease with denatured alcohol, and apply clear finish right away before any oxidation can start. After cleaning, they should not be handled with bare hands, as fingerprints show easily. If old finish needs to be removed, paint remover makes quick work of it.