Lighted fans come with either 3-pin or 4-pin types of Motors, plus LIGHTS mounted in the fan frame. These are completely separate, so you really have TWO devices in one unit, and the each have their own separate cable to supply power and control.
The LIGHTS come in two different types. The simpler plain RGB uses a connector on its cable with FOUR holes. The more complex type called Addressable RGB or ADDR RGB or ARGB or Digital RGB uses a connector with THREE holes (looks like it had 4 but one is blocked) and can do fancier displays including rainbows. A note of CAUTION: the labels "3-pin" and "4-pin" often are used BOTH for the MOTORS and for the LIGHTS, but there is NO relationship. Motors and Lights are separate. So, be sure WHICH type of LIGHTS you have when you ask about "RGB Fans".
Very commonly people plug the motor and the fan cable from a lighted fan into mobo headers for each of those functions, but your mobo needs to have the right header for the lights you have. If you have that, the mobo will come with a software utility to control the lights via the header. If not, you can get third-part Light Controllers for each light type. Some of these have wired or battery-powered control boxes with buttons fo set the light displays manually. SOME come with their own software utility so you can control the fan light from your keyboard and screen. For that last type, the system uses a connection to a mobo USB2 header as a communication channel between that software on the mobo and the Controller box. Commonly that Controller is for LIGHTS only, but SOME such Controllers actually contain TWO Controllers in one box - one for the fan MOTORS and one for the LIGHTS. The USB connection does NOT provide any power to this Controller - it gets all its power from a connection to your PSU. So, whether the Controller you buy does BOTH jobs or just one (leaving the other to mobo headers) will determine how your fan MOTORS and LIGHTS are controlled.
The USB2 header splitter device linked by hotaru.hino above will allow you to convert one mobo USB2 header into two such headers, giving you the extra header you need to make a USB cable connection to a third-party Controller box. This use requires only slow data transfer rates, so splitting one mobo header into two has no negative impact.