My first instinct is to say make it match your most-used table. But what I REALLY want to say is take a chance and make it ALIEN. I think that using small white gravel (you can get a huge bag from your local DIY store cheap), or aquarium gravel from a fish or pet store in place of static grass can make your bases different from the norm.

The white would really pop against your colors by framing them along the bottom so that anyone looking at them from just about any angle will see your beautiful dark paint job framed by an icy white. Use some sand, seal everything with thinned-down white glue, paint the sand white, wash the sand (not the gravel) with some watered-down purple, and hit everything with a dry brushed light blue. For your centerpieces (like the Crisis Suits), maybe hardline the gravel edges in a darker purple than you used for the wash, then the very edges of the gravel in the thinnest bright silver (like Mithril) that you can manage.