If you don't have built-in RGB support then you would be looking at an RGB fan controller.
There are two types, typically. With both you typically plug the controller into one of the fan headers so that the fan speed can be controlled by the motherboard. The lighting will be controlled by the module. This can be completely independent and have a remote control to change colors to fixed settings and patterns, or can be USB based and have software you load into the OS. The USB ones will plug into an available USB 2.0 header on the motherboard.
As for which one you need, would depend on the fans. Some are proprietary and only work with fans that come with them, but there are several standards out there. Aura Sync(ASUS), RGB...