Sealant for Mahogany?

Hi,I am making solid mahogany internal window shutters, the wood has sanded to a beautiful light colour(like beech) I want to retain that look but on tests anything I apply darkens the wood,clear poly varnish,danish oil etc,what can I use without affecting the light colour.The windows are North facing but the house is constantly hot and dry I have to seal the wood or end up with banana shutters half the size I made them within days.Any advice please.