That smudge you see isn't necessarily from the platform but probably more likely from the plant. For some reason some of the plants will created a deep shadow like that. VERY annoying. The only two ways I've found to fix it is either a light that shines pretty much on that area, (like the snake light used for paintings or overhead gallery lights), or choosing a different plant. Try removing one of the plants, either the dogwood, (pink one), or the feathery looking one, one at a time to see which one is creating the shadow.