As part of our terrarium setup I want to include a small PVC pipe extending up through the substrate, for siphoning off water from the false bottom. I want to color it in some way so that it will be unobtrusive, but I want to be sure I use a material to color it that will be safe for the frogs. Is it safe to use a spray paint such as Krylon Fusion, or should I coat it with a dark-colored silicone instead?