By default, all client traffic is tunneled back to the controller. Clients are not aware of the ip address scheme of the physical access points that they are on. The access points only exist as a transport to get client traffic back to the controller. After it get to the controller, client traffic is placed on whatever VLAN is defined in the Virtual AP. That VLAN number determines the VLAN of the client traffic and what default gateway the client has.
For example, if the Virtual AP VLAN is 6, the client traffic is tunneled back to the controller and sent out the trunk between the layer 3 switch and the controller on VLAN 6. The client default gateway is the ip address of the layer 3 switch on VLAN 6.
I hope that makes sense.