hmmm..... well for me having a light colored background just makes my tigers color a bit more lighter.....
actually i tried black/blue/no BG at all and it seems that if your tiger is really unstable changing the background wont help....
for me stability of tigers really depends on water quality, tankmates and environment(driftwood/sand/etc) so for me i would pay more attention to these 3 rather than thinkering with the background...