REAL off camber subject to this topic.. blue and black are the interchangeable colors to the WATER element in Chinese medicine.. either is acceptable...
if ur loking to have a harmonized tank... read a lil about feng shui..
the earth element is contained in the rectangular shape of the tank AND the substrate, water is obviously the water element PLUS the back ground color, all tahts needed is metal, wood and fire....
wood is solved easily with driftwood, the fire element can either be "firey" fish or the color red, and metal is the color white or silver... .. just some food for thought