It's idea is to blush or intensify the color, using PL and/or Nan lighting, I think in the americas a T-5 colormax or aquaglo( something with a good rating from 6500-10000 K) tubes is comparible. I haven't tried it myself, but I have followed it for a while and it seems to work for most people. I tend to think that alot of the gain is the arowana's color developing anyways over that period of time, but like I said I'm no tanning expert. I have seen some fish after tanning, and they are very impressive, and I have seen fish with no tanning look just the same.
The lights purpose:
To stimulate the production of chromatphores, this is what give the contrast between the rim and base colors. Basically it amplifies melanophores on the scales turning light yellow to dark yellow, and the same for orange and pink colors.
This process is also known to be stressfull on the fish, so caution is advised.
Good Luck,