I've been trying desperately to find a game that I only ever played a trial version of that I got from downloads.com around 2004.
Basically, your avatar rides around the map on a mount that changes depending on the color you choose. The gameplay is very reminiscent of Magic: the Gathering in that it uses the same colors, green=nature/swarms, white=angels/defense, red is destruction/direct damage, etc. As you roam around the map you find treasure guarded by monsters, and when you approach a monster it triggers a battle. Different monsters have different allotments of "spells", and you duel each monster to win new spells, exp., and treasure.
I specifically remember the green hero utilizing some kind of woodling creatures that got bigger and gained regeneration as you cast the more expensive ones. I'm pretty sure there were wasps/bees as a flying option for green, as well.
The game is probably pretty obscure, but this is the internet, so nothing is ever too obscure I hope.