It's weird.. In the Colosseum, I haven't gotten golds in a few days. The odd thing is, before this, I got golds with some level 5-7 dragons. But now, my level 10 cold dragon only got silver in a cold event, same thing with my level 10 lightning dragon in a lightning event right after that. I've gotten gold with a level 6 snow dragon in an air event, so what gives? Also, that lightning dragon got a gold in the lightning event when he was level 7.. but not when he was level 10.
I was discussing this with a friend and both of us seem to get the best results by doing the following:
E.g. Water Event
-Highest level dragon: Lvl 19 Panlong -Dragon of the correct element: Panlong = Water, Earth, Fire, Air -Dragon in the habitat that corresponds to the event: I.e. Panlong in Water Habitat.
It could just be an extreme coincidence, but I really think having the Dragon in the same habitat as the event does make Gold more likely. This comes from doing this over several months as well.
For some reason, I seem to have a lot more luck with Panlongs (in the correct habitat) then other hybrids or basic dragons, but I think this just might be a coincidence.
I've read reports from other players that a dragon is more likely to win if the element is there FIRST element (i.e. Water for Panlong, Plant for Bloom, Lightning for Love, Metal for Copper, etc.) but I've never seen a pattern with this with my Panlongs (they get Silver in Water just as often as any other event).
So my method, I use a lvl 15 Panlong each in the respective habitats for the Earth, Fire, Water, Air events. For the Lightning events is use a Love dragon, Bloom for plant and a copper for Metal (all at lvl 15) and I probably win gold 2/3 times on average. I've even gotten runs of 8+ Gold in a row when I was lvl 29 and approaching 30.
I'd suggest that anyone who can't seem to get Gold too often tried the strategies I've mentioned. As I've said, all of the factors might not have any affect, but it definitely can't hurt your chances!