I store my icing in the refrigerator in tupperware containers often. I find that it will separate and needs to be thoroughly mixed again if more than 24 hours has elapsed. Sometimes I will need to add more powdered sugar or thick icing to regain the original consistency. Personally, I haven't had any trouble with spotting or mottling of colors but I live in the desert and it is very dry here. I have used icing that has been stored 2 weeks with no issues. Also, I use meringue powder base.