hehe^.^plants and color of sand/back gound

I suppose it depends on whether you have other "ground cover" that masks the black substrate. In my tank with lots of Val spiralis the substrate is an off-white small gravel (on top of Flourite). But towards the middle and back you don't see the substrate, so it really doesn't matter. Regardless, I think spiral Vals could look good in dark and light substrate.

Remember also that some folks use two different colors of substrate, one for the background where it is more-or-less out of sight, and one for the foreground that is typically lighter color. Amano is known for doing this.

I use dark blue cloth backgrounds and it normally appears black anyway. I think both would work for the color "punch".

A black substrate will make the colors of your plants stand out (mmm, color contrast). White will make both plants and fish seem bleached.

I don't think Vals are heavy root feeders, so substrate fertilization may not be necessary. Unless you have other plants that are root feeders? Otherwise, liquid ferts should be fine.

EDIT: I might be wrong here. I'm looking at several sites and they're giving conflicting info on whether or not Vals are heavy rooters. Need a plant-wiz to confirm please. D:

The plantgeek site says that val spiralis needs a nutrient rich substrate:

http://www.plantgeek.net/plantguide_viewer.php?id=196

I like the look of black backgrounds and black substrate. I also seen some awsome tanks with pale white sand as well. I wanted to go all black, but was unable to get the black substrate I needed and decided on pool filter sand (tan colored) oh well.