How to build an RGB LED circuit?

Recently I modded my old USB mouse by integrating a green LED into it. I have not much knowledge in electricity apart from some Maxwell s equations and standard college curriculum stuff (not the whole two years as I don t even go to college yet). So my plan is to somehow change out the green LED to an RGB one and make a controller that will change the colour (red, green, blue, purple, yellow, brown, white, off) when a momentary switch is activated. So in general a momentary button is pressed and this causes the led colour to change. Thank you in advance and do keep in mind that it has to fit inside a mouse so I can t jam an Arduino inside. Also the USB produces 5V and I connect the circuit in parallel to the mouse circuit.