  Lam and Pylyavskyy introduced loop symmetric functions as a generalization of
symmetric functions. They defined loop Schur functions as generating functions
over semistandard tableaux with respect to a `colored weight,' and they proved
a Jacobi--Trudi-style determinantal formula for these generating functions. We
prove that loop Schur functions can be expressed as a ratio of `loop
alternants,' extending the analogy with Schur functions. As an application, we
give a new proof of the loop version of the Murnaghan--Nakayama rule.
