Get LED lighting for the shimmering effect. In terms of background most people stick to shades of blue and black. its personal choice really. I've seem some really nice blues and blue/grey used, but again its up to personal taste. It's like asking what kind of ice cream flavor is best.
I have 2 tanks with blue and 1 with black. Just wondering if there's anything that geos really stand out on or something. Probably gonna do black or blue again but just like to switch things up
my vote would have to be black just because its darker and makes their colours stand out more imo, blue is dark as well so like others have said, preference.