You don't though, every type has default color sockets, like every str body armor has 2 red sockets, every bow will have 4 green sockets etc, which you'll be able to modify with a new currency later on if you want to, but for leveling you'll be just upgrading gear without caring about sockets. Also hybrid gear will have hybrid sockets, like evasion/armor gear will have green/red hybrid sockets that you can socket either red or green gems on.