Bromides extend the spectral sensitivity a little towards the green, but not much. There may also be an effect using different cations, but again it would be a small effect. Collodion is mainly UV and blue-sensitive, but a pure iodide emulsion will have less spectral sensitivity than one made with a bromide and iodide mix.

It would appear that heavier cations (zinc, cadmium) give a little more spectral sensitivity than lighter ones (potassium, ammonium, sodium, lithium).