The first thing you will notice when looking at one of our bulls is the color of its skin. It's not just for show!
The rarity of your bull has a big impact on how he can play the game, giving him a big boost to his stats, and letting him compete in higher leagues for better rewards. Rarer bulls are also much more expensive to evolve and give you more fusion points when burnt.
Some activities (like mining) are not affected by skin rarity though, so don't worry if you have a brown! They are far from useless in our ecosystem.
Here is a breakdown of skin rarity, with the relevant info on what they impact.
base stats: 5 rarity multiplier (points when burnt): 1 cost to reroll: 1 cost to add attributes: 1 / 2 / 3 / 4
base stats: 20 rarity multiplier (points when burnt): 4 cost to reroll: 2 cost to add attributes: 2 / 4 / 6 / 8
base stats: 100 rarity multiplier (points when burnt): 10 cost to reroll: 4 cost to add attributes: 4 / 8 / 12 / 16
base stats:200 rarity multiplier (points when burnt): 20 cost to reroll: 8 cost to add attributes: 8 / 16 / 24 / 32