jamromhem
Sounds like the white material is really bothering you for some reason. I cant really relate because to see a plant growing in something unnatural, or in a strange location just fascinates me. But if you want something more natural looking, I would suggest using coco coir/chips. The coco coir has a small particle size and looks like the plants are growing in potting soil or peat moss. The coco chips is the same product with the same color, but has a larger particle size. That looks more like the plants are growing in a flower bed that you spread small pieces of pine bark around the planter to look nice.
Growing Mediums for Hydroponic Systems (scroll down to about the middle of the page for pictures of both)
Personally I like using coco chips as my growing media of choice. Not so much because of the way it looks, but because it holds moisture real well, and still allows the roots to be well aerated. It's also easy to work with, and fairly inexpensive, unless you need to have it shipped, then that just about doubles the cost. But I now have a hydroponics shop in town I can get it from, and I also have seen the 2 cubic foot blocks at ACE hardware. The attached picture is the first 2 cubic foot block I ever bought. And the same thing they have at ACE hardware. You can get it for about $10 for a 2 cubic foot block, and that breaks out to about 15 gallons of growing media.