I just finished a grey and red Dodge cake yesterday and as the cake sat out, it developed these lighter discolored dots. At first it wasnt noticeable, but this morning you can really see them. it almost looks like someone splashed a spray of water over the cake, but the cake was in a box, so that for sure didnt happen.What is this from??Is it my fault? The form and decorating of the cake is perfect, so I need to know- should I offer to take some money off the total?

If your buttercream recipe uses salt, it might be that the salt didn't dissolve well before you put it on your cake. I had this problem, but solved it by using a recipe where you totally dissolve the salt in the liquid you add to the buttercream. It hasn't happened since.